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Forschungszentrum Jülichin der Helmholtz-Gemeinschaft
Geschäftsbereich Sicherheit und StrahlenschutzZentralabteilung für Chemische Analysen
Determination of long-lived radionuclidesat ultratrace level using advanced massspectrometric techniques
Myroslav Zoriy
Jül-
4187
Berichte des Forschungszentrums Jülich 4187
Determination of long-lived radionuclidesat ultratrace level using advanced massspectrometric techniques
Myroslav Zoriy
Berichte des Forschungszentrums Jülich ; 4187ISSN 0944-2952Geschäftsbereich Sicherheit und StrahlenschutzZentralabteilung für Chemische Analysen Jül-4187(Diss., Prag, Univ., 2005)
Zu beziehen durch: Forschungszentrum Jülich GmbH · ZentralbibliothekD-52425 Jülich · Bundesrepublik Deutschland� 02461 61-5220 · Telefax: 02461 61-6103 · e-mail : [email protected]
i
Abstract
Determination of long-lived radionuclides at sub-fg concentration level is a challenging
task in analytical chemistry. Inductively coupled plasma mass spectrometry (ICP-MS)
with its ability to provide the sensitive and fast multielemental analysis is one of the most
suitable method for the measurements of long lived radionuclides in the trace and ultra
trace concentration range.
In present the Ph.D. study a variety of procedures have been developed permitting the sub
fg ml-1 determination of long-lived radionuclides (e.g. U, Th, Pu) as well as 226Ra (T1/2 =
1600 y) and 90Sr (T1/2= 28.1 y) in different samples. In order to avoid isobaric
interferences, to increase the sensitivity, precision and accuracy of the methods the
application of different techniques: pre-concentration of the sample, off-line separation
on the crown resin, measurements under cold plasma conditions, using microconcentric
nebulizers (e.g DIHEN, DS-5) or the application of LA-ICP-MS for sample introduction
have been studied.
The limits of detection for different radionuclides was significantly improved in
comparison to the ones reported in the literature, and, depending on the method applied,
was varied from 10-15 to 10-18 g ml-1 concentration range. For instance, the LOD for 239Pu
in 1 l of urine, based on an enrichment factor (due to the Ca3(PO4)2 co-precipitation) of
100 for PFA-100 nebulizer and 1000 for DIHEN, were 9×10?�18 and 1.02×10?�18 g ml?�1,
respectively.
239Pu was detected (after the enrichment) in 100L of the Sea of Galilee at a concentration
level of about 3.6 × 10-19g ml-1 with a 240Pu/239Pu isotope ratio of 0.17. This measured
plutonium isotope ratio is the most probable evidence of plutonium contamination of the
Sea of Galilee as a result of global nuclear fallout after the nuclear weapons tests in the
sixties.
ii
A sensitive analytical procedure based on nano-volume flow injection (FI) and
inductively coupled plasma double-focusing sector field mass spectrometry (ICP-SFMS)
was proposed for the ultratrace determination of uranium and plutonium. A 54-nl sample
was injected by means of a nano-volume injector into a continuous flow of carrier liquid
at 7 ?�L min-1 prior to ICP-SFMS. The absolute detection limits were 9.1×10-17 g (3.8 ×
10-19 mol, ~230 000 238U atoms) and 1.5 × 10-17 g (6 × 10-20 mol, ~38 000 242Pu atoms)
for uranium and plutonium, respectively.
The 90Sr, 239Pu and 240Pu at the ultratrace level in groundwater samples from the
Semipalatinsk Test Site area in Kazakhstan have been determined by the developed ICP-
SFMS method. In order to avoid possible isobaric interferences at m/z 90 for 90Sr
determination (e.g. 90Zr+, 40Ar50Cr+, 36Ar54Fe+, 58Ni16O2+, 180Hf2+, etc.), the measurements
were performed at medium mass resolution under cold plasma conditions. Pu was
separated from uranium by means of extraction chromatography using Eichrom TEVA
resin with a recovery of 83%. The limits of detection for 90Sr, 239Pu and 240Pu in water
samples were determined as 11, 0.12 and 0.1 fg ml?�1, respectively. Concentrations of 90Sr
and 239Pu in contaminated groundwater samples ranged from 18 to 32 and from 28 to 856
fg ml?�1, respectively. The 240Pu/239Pu isotopic ratio in groundwater samples was
measured as 0.17, which indicates the most probable source of contamination - nuclear
weapons tests at the Semipalatinsk Test Site conducted by the USSR in the 1960s
The LA-ICP-MS was used in present work for the determination of naturally occurred
long lived radionuclides (e.g. U, Th) in different kinds of solid samples (2D gel of
separated proteins, thin cross section of human brain tissue, biological samples [flower
leafs]). An unique cooled laser ablation chamber (using two Peltier elements) was
designed for these experiments. Using this chamber the precision and accuracy of the
measurements were improved up to one order of magnitude and was found to be very
advantageous in comparison to the non-cooled laser ablation chamber. The precision of
the measurements of e.g. uranium isotope ratios in the range of 2.0–1.6% for 234U/238U,
1.3–0.4% for 235U/238U and 2.1–1.0% for 236U/238U in selected uranium isotopic standards
reference material were determined by microlocal analysis (diameter of laser ablation
iii
crater: 15, 25 and 50 ?�m) using LA-ICP-MS with a cooled laser ablation chamber. The
accuracies of 234U/238U, 235U/238U and 236U/238U isotope ratios varied in the range of 4.2–
1.1%, 2.4–0.5% and 4.8–1.1%, respectively, and were dependent on the diameter of the
laser beam used.
In addition to the analysis of long lived radionuclides, some other elements, that can
present potential interest to the analyzed sample, were measured within the framework of
the present study. Laser ablation inductively coupled plasma mass spectrometry (LA-
ICP-MS) was used to produce images of element distribution in 20-?�m thin sections of
human brain tissue. The sample surface was scanned (raster area ~80 mm2) with a
focused laser beam (wavelength 213 nm, diameter of laser crater 50 ?�m, and laser power
density 3×109 W cm-2) in a cooled laser ablation chamber developed for these
measurements. Cross sections of human brain samples – hippocampus as well as brain
tissues infected and non-infected with Glioblastoma Multiforme (tumor cells) were
analyzed with the developed procedure. An inhomogeneous distribution (layered
structure) for P, S, Cu, and Zn in thin brain sections of the hippocampus were observed.
In contrast, Th and U were more homogeneously distributed at a low-concentration level
with detection limits in the low-ng g-1 range.
P, S, Si, Fe, Cu and Zn were measured by LA-ICP-MS in human brain proteins, separated
by 2D gel electrophoresis. Quantification procedure was carried out using the sulphur
(determined by MALDI-FTIR-MS) as an internal standard. In addition to the essential
elements, U and Th were determined in some proteins spot in 2D gel electrophoresis. The
LODs of 0.01 ?�g g-1 for both radionuclides were observed.
iv
Contents
1. Motivation of the work
2. Measurements techniques for determination of long-lived radionuclides
2.1. Overview of most important techniques for long lived radionuclides determination (e.g RIMS, AMS, TIMS etc)
2.2. Capability of ICP-MS for analysis of long lived radionuclides. 3. Fundamentals and principle of ICP-MS
3.1. Sample introduction system 3.2. Ion generation in inductively coupled plasma 3.3. Ion extraction 3.4. Ion separation in mass analyzer 3.5. Ion detection
4. Separation and pre-concentration methods
4.1. Possible on-line separation (Capillary electrophoresis (CE) separation) 4.2. Off-line separation (extraction chromatography, co-precipitation) 4.3. Pre-concentration methods
5. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)
5.1. Application of LA-ICP-MS for determination of long lived radionuclides 5.2. Basics and instrumentation of LA-ICP-MS
6. Experimental part
6.1. Instrumentation
6.1.1. Optimization and experimental parameters of double focusing ICP-MS (ICP-SFMS)
6.1.2. Advanced solution introduction systems (Aridus, USN, DIHEN, nano-FI-ICP-MS)
6.1.3. Laser ablation ICP-MS 6.1.3.1. Experimental parameters of LA-ICP-MS 6.1.3.2. LA-ICP-MS with cooled LA-chamber
6.2. Quantification and evaluation of analytical data
v
6.2.1. External calibration using standards reference materials 6.2.2. Standard addition method 6.2.3. Isotope dilution analysis 6.2.4. Solution based calibration in LA-ICP-MS
6.3. Samples preparation
6.3.1. Pre-concentration of actinides 6.3.1.1.Co-precipitation of actinides with MnO2 and Fe(OH)3 from large
volumes of water samples 6.3.1.2.Co-precipitation of actinides with Ca(PO3)2 from urine samples 6.3.1.3.Co-precipitation on crown ether resins
6.3.2. Samples separation from complex matrices
6.3.2.1.Extraction chromatography protocols
6.3.2.1.1. Actinide separation on TEVA-resin 6.3.2.1.2. Actinide separation on UTEVA-resin 6.3.2.1.3. Separation of Sr on “Sr-specific” resin 6.3.2.1.4. Ra separation on “Ra specific” disk
6.3.3. Sample preparation procedure for ICP-SFMS measurements of urine
samples
6.4. Isotopes standards, standard reference materials and chemicals
7. Results and discussions
7.1. Methodical development for analysis of actinides by ICP-SFMS
7.1.1. Improvement of LOD for 236U and minimum 236U/238U detectible isotope ratio
7.1.2. Minimization of necessary sample volumes for ICP-MS actinide analysis
7.1.2.1. DIHEN-ICP-MS measurements of uranium standard isotopic reference materials
7.1.2.2. Application of nano-FI-ICP-MS for determination of actinides at ultratrace concentration level
7.2. Determination of long lived radionuclides at ultratrace concentration level by ICP-MS
7.2.1. Determination of plutonium, americium and 237Cs at ultratrace level in
soil samples
vi
7.2.2. Determination of Pu at at ml-1 level in urine 7.2.3. 226Ra determination in mineral water samples 7.2.4. Routine determination of naturally occurred long lived radionuclide in
urine
7.3. Isotope ratio measurements of long lived radionuclides by ICP-MS
7.3.1. Pu isotope ratio measurement in environmental sample 7.3.2. Routine determination of 234U/238U and 235U238U isotopic ratios in
urine samples.
7.4. ICP-MS determination of 90Sr
7.4.1. Improvement of LOD for 90Sr by decreasing of background signal on m/z 90
7.4.1.1.Cold plasma technique 7.4.1.2.Application of medium mass resolution mode (R=4000)
7.4.2. Determination of 90Sr in environmental samples
7.5. LA-ICP-MS as important ultrasensitive techniques for determination of long
lived radionuclides and their isotopic ratios in solid samples
7.5.1. Application of solution based calibration LA-ICP-MS for actinide determination in Nist 612 glass standard reference material
7.5.2. Determination of U and Th by ID-LA-ICP-MS in faeces samples 7.5.3. Determination of U isotopic ratio on the surface of biological samples
using cooled LA chamber for LA-ICP-MS
7.6. Application of LA-ICP-MS for actinide determination in single proteins separated by 2D gel electrophoresis
7.7. Lateral distribution of concentrations of actinides as well as some other
elements in thin cross section of brain tissue measured by LA-ICP-MS 7.7.1. Human brain samples
7.7.1.1. Hippocampus region 7.7.1.2. Brain cancer region
8. Conclusions and outlines 9. References
1. Introduction
1.1. Motivation of the work
Analysis of long-lived radionuclides is required in many application fields [1-5] such as
environmental monitoring, nuclear forensic studies and nuclear safeguards, decontamination and
environmental remediation, nuclear waste characterization (radioactive waste control) and
management of radioactive waste of high radiological toxicity for storage and disposal. The
determination of long-lived radionuclides, therefore, has become of increasing importance,
especially in environmental materials such as waters [6, 7], in geological and biological sample
[8-10], in medical samples [11, 12] nuclear material and radioactive wastes and high-purity
materials [13, 14] ceramics and glass [15]. Furthermore, isotope ratio measurements of long-lived
radionuclides are of additional interest. For instance, isotope ratio measurements of uranium and
plutonium can indicate the origin of contamination in the environmental samples [16, 17]; the
determination of possible isotopic variation in nature due to the radioactive decays of unstable
nuclides has been applied in geochronology for age dating, based on the decay of natural-lived
radionuclides (e.g. 232Th, 235U, 238U, etc) [9, 18]; precise and accurate determination of isotopic
ratio measurements is also required for isotopic dilution study, where the relative standard
deviation of the method can be improved lower than 0.05 % [19, 20]. 236U can be used as a
powerful tool for ‘‘fingerprinting’’ of artificial uranium in environmental samples and the
relatively large increases in the 236U/238U isotopic ratio represent sensitive indicator of the
presence of irradiated uranium [16, 21-23]. Boulyga et al. [16] studied the 236U isotope to monitor
the spent uranium from nuclear fallout using inductively coupled plasma mass spectrometry
(ICP-MS) in soil samples collected in the vicinity of the Chernobyl Nuclear Power Plant. The
concentration of Chernobyl spent uranium in upper (0-10 cm) soil layers in investigated areas in
the vicinity of Chernobyl NPP amounts to 2.4×10-9 g g-1 to 8.1×10-1 g g-1 depending mainly on
the distance to the Chernobyl reactor. 226Ra has been recognized as one of the most toxic natural radioelement. Furthermore, because of
its similarity to the alkaline earth metals, radium follows the calcium pathway in biological
organisms, so it is strongly adsorbed into bones, cell and tissues where its counting activity may
cause serious damage [24, 25].
1
Of special interest, is the determination of radioactive 90Sr because of its impact in both
environmental and health areas. In the environment Sr deposition mainly occurs with rain or
other precipitation and the strontium is very accessible to plants via soil uptake mechanisms [8].
In addition, strontium belongs to the same group of metals as calcium, which represents the
principal source of danger. When the 90Sr is ingested or inhaled, it processed by the body in the
same way as calcium and accumulates in bones or teeth (about 20-30% of total ingested 90Sr). In
the human body radioactive 90Sr can ionize molecules by the emission of a medium energy β-
particle of 0.5 MeV (specific activity of 90Sr is about 5.1×1012 Bq g-1) creating the risk of cancer,
especially bone cancer and leukemia. It decays into 90Y, which is also a β-emitter and is normally
in equilibrium with 90Sr, thus doubling the specific activity of the material.
Accumulated in bone and teeth 90Sr can be used as a powerful tool for age determination [26, 27].
For instance, Tolstykh et al. [11] studied age dependencies of 90Sr incorporation in dental tissues
by measurements of 90Sr in the teeth of residents living in settlements along the Techa River.
Nowadays the development of analytical methods for the analyzing of long lived radionuclides at
ultratrace concentration levels (e.g. high radioactive materials from nuclear reactors) is focused
on improving microanalytical techniques in order to reduce the sample volume (minimize
radioactive contamination of instruments and dose to the operators), or improve the detection
limits, the precision (relative standard deviation, R.S.D.) and accuracy of the measurements.
Routine methods for the determination of long lived radionuclides are of additional importance.
The analytical procedures developed should serve to save the time and cost of the analysis as well
as be easy to the operators.
The research of this Ph.D. thesis has been focused on development of advanced analytical
methods permitting the determination of long lived radionuclides such as Ra, Th, U and Pu and
their isotopic ratios at the ultratrace concentration range. Different preparation and measurement
procedures (e.g. sample separation and pre-concentration, micronebulization, etc) have been used
in order to improve the figures of merits of ICP-MS actinide analysis.
As a part of the work the performance of ICP-MS in determination of 90Sr radionuclide was
studied. The method developed was applied to the test urine samples and ground water samples
from the contaminated areas.
2
In addition, the capability of LA-ICP-MS was evaluated for the screening and mapping analysis
of naturally occurred radionuclides, such as Th and U in the separated proteins and different
medical tissues.
3
2. Measurement techniques for determination of long-lived
radionuclides
2.1. Overview of most important techniques for long lived radionuclide
determination For many decades, there has been a range of well-established measurements techniques that are
excellent tools for the trace, ultratrace and surface analysis of long lived radionuclides in different
kind of samples.
The principle of radioanalytical methods is based on the direct measurements specific activity of
selected radionuclide. Because of the type of emission, the methods are divided on the α-, β and
γ-spectrometry. At present the radiometric techniques are mainly used for the analysis of short
lived radionuclides and their application in this area has found to be very effective [11, 21, 28-
30]. For instance, the strong γ-emission of 137Cs can be measure by γ-spectrometry without any
additional sample preparation steps with high precision and accuracy up to sub-fg ml-1
concentration level. However for the characterization of radionuclides with the half-life time
higher than 104 years (e.g 235U, 238U with the T1/2= 108 and 109 y, respectively) the radioanalytical
analysis usually becomes more difficult, due to the necessity of careful chemical separation and
enrichment of analyte, that are mostly labor- and time -consuming. However, the major
disadvantage of application of radioanalytical methods for determination of long lived
radionuclides relates to the counting period time, which can take from the few days to several
weeks, depending on the sensitivity required [31]. In addition, because of the similarity of the
emission energy, the certain radionuclides can not be resolved using radiometric techniques (e.g. 239Pu and 240Pu with α-energies of 5.24 and 5.25 MeV, respectively) [32, 33].
Mass spectrometric techniques have the advantages in comparison to the radiometric techniques
for the analysis of long-live radionuclides. These include a shorter analytical time, an
improvement in analytical precision and a reduction of the required for the analysis sample size.
For determination of radionuclides in aqueous solution the Thermal Ionization Mass
Spectrometry (TIMS), Accelerator Mass Spectrometry (AMS), Resonance Ionization Mass
Spectrometry and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) are used in many
4
analytical labs. As an example, in the Fig. 1.1 the numbers of works for determination of long
lived radionuclides by radioanalytical methods and e.g. ICP-MS in the last 5 years is compared.
020406080
100120140160
2000 2001 2002 2003 2004 2005year
num
ber o
f pub
licat
ions
Radioanalytical methodsICP-MS
Fig 1.1. Comparison of the numbers of publications of determination of long lived radionuclides by ICP-MS and radioanalytical method in the past 5 years
TIMS [34, 35] as precise isotope analytical technique, is applied mainly in geological studying.
For example, Lamont et al. [36] have analyzed 230Th/234U isotopic ratio for age determination of
uranium materials using isotope dilution TIMS. However, the complex sample preparation steps
as well as quantification procedure are the serious disadvantage of this mass spectrometric
technique.
Using AMS [37, 38] the lowest limit of detection can be achieved for radionuclide determination.
Paul et al. [7] determined the 90Sr limit of detection in the water solution of about 2-4 107 atoms
of 90Sr, but the capital costs and centralized placement of AMS facilities restrict its use to
specialized applications.
As an alternative to AMS, RIMS was recently established for determination of different
radionuclides at ultratrace level [39, 40], but at present RIMS instruments are not available on the
analytical market.
For the solid state mass spectrometry, where the analytical investigation are focused on trace and
ultratrace analysis on bulk materials and layers, contamination on substrates, determination of
stoichiometry, inclusion or impurities, the inorganic mass spectrometric techniques such as
SIMS[41, 42], GDMS [43, 44], SNMS [45], as well as Laser Ablation ICP-MS (LA-ICP-MS) are
successfully utilized. Thus, Tambroni [46] applied the SIMS for characterization of particles of
interest containing mainly U and other actinides in different samples. The successful
5
identification of uranium and plutonium particles and determination their isotopic composition
have been performed.
2.2. Capability of ICP-MS for analysis of long lived radionuclides
Inductively coupled plasma mass spectrometry (ICP-MS) exhibits high sensitivity, good accuracy
and precision of isotopic measurement as well as a relatively easy sample preparation
procedure[3, 47, 48]; and, arguably, is one of the most suitable methods in atomic spectrometry
for determination of long lived radionuclides in aqueous solution at ultratrace concentration level.
On solid materials ICP-MS can be also applied after sample digestion. In contrast to the inorganic
solid mass spectrometric techniques, ICP-MS allows a simple sample introduction in a normal
pressure ion source and an easy quantification procedure using aqueous standard solution. In the
Table 2.1 the capability of ICP-MS for ultratrace and isotope analysis of long-lived radionuclides
in comparison to the other analytical methods is summarized.
Table 2.1. Capability of ICP-MS for determination of long-lived radionuclides in comparison to the other analytical techniques
Analytical
method
Detection limit
g g-1
Multielemental
capability
Reference:
α-, β, γ-
spectrometry
4×10-10 (238U), 2×10-13 (237Np)
2×10-15 (239Pu), 3×10-17 (241Am)
6×10-13 (239Pu)
1×10-12 (239Pu), 0.1×10-12 (240Pu)
+
Dacheux et al.[49]
LaMont et al[50]
Hrnecek et al[51]
RIMS 3.9×10-16 ( 236U, 239Pu) - Trautman et al[52]
AMS 1.3×10-12 (236U)
1×10-11 (236U)
4.02×10-16 (239Pu)
4×10-17 (244Pu)
-
Danesi et al.[53]
Berkovits et.al.[54]
Fifield et al.[55]
Vockenhuber et al.[56]
TIMS ~1×10-13 (238U, 236U)
6×10-12 ( 236U)
26×10-15 ( 239Pu)
(+)
Sahoo et al.[57]
Richter et al.[58]
Inn et al.[59]
ICP-MS 0.2×10-15 (236U,), 0.2×10-15 (239Pu)
4.7×10-15 (239Pu)
0.6×10-15 (239Pu), 0.2×10-15 (240Pu)
2×10-14 (239Pu, 241Am)
++
Boulyga et al.[60]
Ting et al.[61]
Kim et al.[62]
Evans et al.[63]
6
Nevertheless, the analytical figures of merit of ICP-MS are limited by influence of mass
spectroscopic interferences on the analyte ions. These are isobaric atomic ions, multiply charged
ions and molecular ion of various origins, which occurs at the same nominal mass as analyte ions
and the mass resolution of available ICP-MS in not enough to resolve them. Therefore, an
alternative approach should be applied to separate the analyte ions from interfering ones.
ICP-MS offers some interesting advantages to solve these inherent interference problems.
Isobaric interferences can be resolved using double-focusing sector field ICP-MS at the required
mass resolution. Furthermore, by the application of ICP-MS with collision cell, disturbing
interfering isobaric ions can be suppressed or special sample introduction and coupling
techniques such as high-performance liquid chromatography (HPLC) and capillary
electrophoresis (CE) can be helpful to avoid interference problems by separating the analytes.
Based on the mass separation analyzer the different commercial double focusing sectors field
ICP-MS with single or multiple collectors (e.g. “Element”, “Element2” “NEPTUNE”
(ThermoElectron, Bremen, Germany), “Axiom” (VG Elemental, UK) and “JMS-Plasma X2”
(Joel, Japan); quadrupole-based ICP-MS without and with collision cell (e.g. Perkin Elmer Sciex,
Agilent, Varian GmbH analytical instruments, Micromass); a time-of-flight ICP-MS from Leco
and single magnetic sector field ICP-MS with collision cell ‘Nu Plasma’ (Nu Instruments) are
available on analytical market. In Table 2.2 the detection limits for the determination of long-
lived radionuclides measured by ICP-MS are compared with those of solid mass spectrometry.
The mass resolution of double focusing sector field instruments usually can be varied, (e.g for
“Element” ICP-SFMS the mass resolution m/Δm can be set upped on 300, 4000 and 12000 for
low-, medium- and high mass resolution setting, respectively), while for quadrupole based ICP-
MS m/Δm is about 400. In the low-resolution mode, the element sensitivity of commercial
double-focusing sector field ICP-MS is significantly higher than conventional quadrupole ICP-
MS. The extreme element sensitivity of double-focusing sector field ICP-MS permits ultratrace
analysis down to the sub-fg mL-1 concentration range [47].
Whereas the precision for isotope ratio measurements in quadrupole ICP-MS varies between 0.1
and 0.5%, double focusing sector field ICP-MS with single ion detection allows isotope ratio
measurements with a precision of 0.02% [64]. A better precision of isotope ratio measurements
of isotope ratio measurements (one order of magnitude) was achieved by the introduction of the
multi-ion collector device in sector field ICP-MS. For instance, Ehrlich et al. [65] measured a
7
lead and uranium isotope ratios in two types of Mn nodules from the Cambrian Timna Formation,
Israel.
Table.2.2 The limits of detection for different mass spectrometric techniques for determination of long-lived
radionuclides[64]
Analytical method Detection limit
Solid state mass spectrometry (μg g-1)
SSMS 1-0.001
GDMS 0.1-0.0001
SIMS 10-0.002
LA-ICP-MS 0.010-0.00001
ICP-MS (ng l-1)
Quadrupole ICP-MS 0.01-0.6
ICP-SFMS (m/Δm = 300) 0.00004-0.005
ICP-QMS with collision cell 0.003-0.01
ICP-TOFMS 0.1-1
MC-ICP-MS (sector field) 0.0001-0.0002
The values for the 207Pb/206Pb and 208Pb/206Pb ratios have been determined with precisions of up
to 50 ppm (0.005%R.S.D.) and those of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb - up to 200 ppm.
The values for the 234U/238U ratios have been determined with precisions of 0.4-1%.
3. Fundamentals and principle of ICP-MS
From the about 20 years of commercialization, ICP-MS has becomes the most successful method
in many analytical laboratories for the accurate and precise isotopic determination for different
applications field required nowadays. There are a number of different ICP-MS designs
commercially available today, each with their own strengths and weaknesses. They all share
many similar components, like nebulizer, spray chamber, plasma torch, interface and detector,
but can differ quite significantly in the design of the mass spectrometer and in particular the mass
separation device. Generally, the principle of ICP-MS method can be subdivided in the following
8
regions: (i) sample introduction, (ii) atomization (iii) ion extraction, (iv) ion separation and (v)
ion detection [48] (see Fig. 3.1.).
Fig 3.1. Basic Instrumental Components of ICP-MS
MSInterface
Ion Detector
ICP Torch
3.1. Sample introduction system
The sample introduction is one of the most important processes in ICP-MS method. Based on the
different sample form (liquid or solid) there exist different sample introduction systems for ICP-
MS. If the analyzed sample is presented in the liquid form, the sample solution is pumped with a
peristaltic pump into a nebulizer, where it is converted into a fine aerosol with argon gas at about
1 L/min. As an example, in the Fig. 3.2 the schematic view of the microconcentric nebulizer
(MCN-100) is shown.
Mass Separation analyzer e.g. quadrupole, double focusing analyzer, etc
RF PowerSupply
Nebulizer
MechanicalPump
Turbo Molecular
Pump
Turbo Molecular
Pump
Ion OpticsSpray
Chamber
9
Nebulizer gas
Sample introduction
Fig 3.2. Schematic arrangements of microconcentric nebulizer (MCN-100)
At the present, commercially exist the variety of nebulizer’s with different kind and construction.
Usually, nebulizer can be classified on the type of energy that is employed for aerosol
production:
• by kinetic energy of high velocity gas stream (Meinhard [66], and Cross-Flow
nebulizer [67]) that mainly applied with combination with spray chamber (e.g. “Scott-
Type”) or with desolvation systems (e.g. “Aridus” [16]).
• as the result of mechanical energy applied externally through a rotating or vibrating
(“Ultrasonic nebulizer” [68])
• as a result of the mutual repulsion of charges accumulated on the surface (electrostatic
nebulizers).
The most common type of nebulizers used - pneumatic nebulizers, due to the easiness of
operation and stability of aerosol production. In addition, on the analytical market
microconcentric nebulizers, such as Direct Injection High Efficiency Nebulizer (DIHEN) [69]
and DS-5 [70] were introduced, that allow to decrease the volume of sample needed for
measurements to sub-μl range.
For the introduction of solid sample usually laser ablation ICP-MS (LA-ICP-MS) [15, 71-74] or
electrothermal vaporization ICP-MS (ETV-ICP-MS) [75-77] are applied.
10
3.2. Ion generation in inductively coupled plasma
The fine droplets of aerosol produced by nebulizer, which represent from 2 to 20% of the sample
(depending of the nebulizer type), are separated from larger droplets by means of a spray
chamber or by desolvation system and transported into the ICP torch via a sample injector. The
plasma in the torch is formed by the interaction of an intense magnetic field (produced by RF
passing through a copper coil) on a tangential flow of gas (normally argon), at about 18 L/min
flowing through torch. The chemical compounds of the sample contained in the aerosol are
decomposed into their atomic constitutes in the inductively coupled plasma and ionized at a high
degree of ionization (>90% for most chemical elements) with the low fraction of multiply
charged ions (~1%) [5].
Between the RF coil and the plasma, there is a capacitive coupling, producing a potential
difference of a few hundred volts. If this wasn’t eliminated, it would result in an electrical
discharge (called a secondary discharge or pinch effect) between the plasma and the sampler
cone. This discharge increases the formation of interfering species and also dramatically affects
the kinetic energy of the ions entering the mass spectrometer, making optimization of the ion
optics very erratic and unpredictable. For this reason, it is absolutely critical that the secondary
charge is reduced, by using some kind of RF coil grounding mechanism. There have been a
number of different approaches used over the years to achieve this, including a grounding strap
between the coil and the interface, balancing the oscillator inside the RF generator circuitry, a
grounded shield or plate between the coil and the plasma torch, or the use of a double interlaced
coil where RF fields go in opposing directions. They all work differently, but basically achieve a
similar result and that is to reduce or eliminate the secondary discharge.
In the inductively coupled plasma various ionisation mechanisms can take place [78]:
1. Electron-Collision ionisation through collisions between electrons and atoms
X + e- X+ + 2 e-
2. Penning –ionisation through collisions between atoms at metastable species
Arm + X Ar + X+ e-
Arm + X Ar + X+(*) + e-
11
3. Charge substitution reaction trough the charge substitution between the ions and
atoms
Ar+ + X Ar + X+
where, X is atom, * and m correspond to the excited and metastable condition of the atom, respectively Different atoms required different ionisation energy. Such difference can be successfully applied
for the improvement of analytical technique, where by the tuning of supplied fr-power selective
separation of analyte from the interfering ions is possible. For instance, Vanhaecke et al., at rf
power of 750 W were able to reduce sufficiently the formation of the 40Ar12C+ diatomic ions that
interfered with the determination of the major chromium isotope at m/z = 52.
3.3. Extraction and focusing of the ions
The ions produced in the plasma, are extracted and directed into the mass spectrometer via the
interface region, which is maintained at a vacuum of about 0.5 Pa with a mechanical roughing
pump. For extraction the ions the negative potential (about -2000V) is applied on the ion optics.
The interface region consists of two metallic cones (usually nickel), called the sampler and a
skimmer cone, each with a small orifice (0.6-1.2 mm) to allow the ions to pass through to the ion
optics, where they are guided into the mass separation device. The ions extraction via the
interface region is one of the most critical areas of an ICP mass spectrometer, because the ions
must be efficiently transported from the plasma, which is at atmospheric pressure (about 1 MPa)
to the mass spectrometer analyzer region at the pressure approximately 5×10-6 Pa.
Extracted from the ICP positively charged ions have the different kinetic energy and therefore,
before the entering the mass analyzer must be focused, usually, with the ion optics. The principle
of such ion focusing (e.g. using the ion lenses) is shown in Fig. 3.3.
The potentials V1 and V2 are different (and lower than Vinitial), so there a non-homogeneous field
is formed (see curved dashed lines). The focusing effect, shown in the Fig 3.3 consist of fact that
the ions, which are going not through the central path of the ion lens, will be deflected by the
electric field and focused in the direction of the central path.
12
+
V initial
Ion source
+
Ion lens
V1 V2
Fig. 3.3. Principle of ions focusing with ion lens in ICP-MS [79]
In all ICP-mass spectrometers the attention should be paid also for of the emitted by plasma
photons that can produce a high background signal when they reach the detector. To minimize
this background, a so-called photon-stop is utilized in the many quadrupole based ICP-MS
instruments. The photon-stop is a small metal plate placed in the centre of the ion beam, which
reflects the photons away from the detector. The positive ions are not stopped by the photon-stop
because the positively charged cylinder lens guides them around it. In other quadrupole-based
ICP-MS the ion optic system is constructed under the defined angle to photon flying path so the
ions is going in a separate way as the emitted by plasma photons. In the double focusing ICP-
SFMS instruments the photons is not reaching the detector due to the curved geometry of the
mass separation system. In comparison to the ICP-QMS the background noise of the detector in
ICP-SFMS instrument is much lower and usually is less than 0.2 cps.
3.4. Ion separation in mass analyzer system
Extracted from the interface region ions, are directed by the ion optics into the mass separation
analyser. The operating vacuum in this region is maintained at about 1 10 -5 Pa with a
turbomolecular pumps.
13
There are many different mass separation devices, all with their strengths and weaknesses. Four
of the most common types are quadrupole, double focusing sector field, time of flight and
collision/reaction cell technology. Because the all work during the present study was performed
using the double focusing sector field ICP-MS the all further explanation will be concerning of
this type of ICP-MS instrumentation.
The physical principles of the double focusing ICP-SFMS fundamentals was in detail described
by Dietze [80]. With the knowledge of the radius of magnetic sector field r as well as the widths
of the entrance and exit slits it is possible to calculate the maximal possible mass resolution of the
magnetic sector field instrument:
)( 21 SS
rm
mR B
+=
Δ= (3.1)
The formula 3.1 assume, however, that the energies of all ions are the equals, so the energy
dispersion ΔδE/qUB (UB – potential difference) of the ions in ICP should be taken into account:
BB qUErSSmmR
//)(1
21 δΔ++≈
Δ= 3.2
The eq. 3.2 shows that with the minimization of energy dispersion of extracted from the plasma
ions it is possible to improve the mass resolution of the instrument. To achieve this a combination
of magnetic and electrostatic field can be applied. Because the energy dispersion of electrostatic
analyzer is opposite to that of the magnetic sector the energy dispersions of the both analyzer will
compensate each other, so that finally only the mass dispersion is left.
Fig. 3.4 presents the schematic view of the combination of magnetic and electrostatic field
(double focusing) of the mass separation system as well as calculated using the “SIMION”
program ion trajectories for m/z 90 u, 100 u and 110 u.
The operation conditions have been chosen in this example so that only ion with a mass of 100 u
can reach the exit slit S2, after which the detector is located (see Fig. 3.4a). In the Fig 3.4b the
calculation were done with the ion energy spread of 500 eV. In this case the ions are not well
focused by the magnet, and for a single magnetic device the resolving power would be worse.
However, with the using of electric sector field after the magnet, the all ions are well focused into
the exit slit owing to the energy dispersion of the electric sector. The combined system focuses
14
the both, the angle and the energy of the ions and this is the reason, why this system calls often
double focusing.
Fig. 3.4. SIMION calculations of ion trajectories in a double focusing mass analyzer with a 90°C magnet operated at 4770 Gauss and a 60°C electric sector with a voltage of + and -410 V; Ua = 8000 V [81]; a) ion trajectories for mass 90, 100 and 110 are shown for monoenergetic ions emerging from the entrance slit S1 with an angle of 7°; b) ion trajectories for mass 100 with an energy spread of 500 eV. Based on the placement order of magnetic and electrostatic analyzers there are exist two type of
double focusing construction arrangements - Nier-Johnson- and reverse-Nier-Johnson-Geometry.
In this work (see Fig.3.5) applied ICP-SFMS was a double focusing sector field instrument with a
reverse Nier-Johnson-Geometry (the magnetic sector is placed before the electrostatic analyzer).
The equation 3.2 shows that the mass resolution of the instrument in determined also by the slit
widths. In the used ICP-SFMS besides the entrance and exit slits the third –intermediate slit is
applied (see Fig. 3.5). With the fully open intermediate slit the instrument is operated in low
resolution mode, which is characterized by the flat-top peak shape. This peak shape is
advantageous if the instrument is operated in a peak hopping mode because small changes in the
mass calibration will still lead to the same intensity value.
15
Figure 3.5: Schematic arrangement of double focusing sector mass spectrometer (reverse Nier –Johnson geometry)
Intermediate Slit
Electron Multiplier Detector
By the decreasing of the peak widths the resolution will be increased (eq.3.2) and the instrument
will be operated in the medium and high resolution modes. Typical mass resolution value R
observed in applied ICP-SFMS instrument at the low, medium, and high mass resolution were
300, 4000 and 11 000, respectively.
3.5. Ion detection
The separated by double focusing mass analyzer ion beam is converted to the electrical signal
with the ion detector. The most common design used today is called a discrete dynode detector or
secondary electron multiplier (SEM), which contain a series of metals dynodes along the length
of the detector. In this design, when the ions emerge from the mass filter, they impinge on the
first dynode and are converted into electrons (see Fig.5.7).
As the electrons are attracted to the next dynode, electron multiplication takes place, which
results in a very high steam of electrons emerging from the final dynode. This electronic signal is
then processed by the data handling system in the conventional way and converted into analyte
concentration using ICP-MS calibration standards. Most detection systems used can handle up to
16
8 orders of dynamic range, which means they can be used to analyze samples from ppt levels, up
to hundreds of ppm.
Fig.5.7. Principle of the amplification of ion signal in secondary electron multiplier
Recently on the analytical market a new unique detection
system, that combines a dual mode SEM with a Faraday
detector, has been introduced with the Finnigan
ELEMENT XR ICP-MS [82]. Using such combination, the
linear dynamic range of the Finnigan ELEMENT XR can be
increased by an additional three orders of magnitude, when
compared to the Finnigan ELEMENT2, to over 1012 (see Fig. 5.8.).
Fig. 5.8. Calibraion curve in extended dynamic range measured in counting, analog and faraday detector mode on the Element XR ICP-SFMS [82].
With this increase in dynamic range,
by measurement in counting, analog
and faraday detector modes, the
maximum measurable concentration
achievable with the Finnigan
ELEMENT XR is over 1000 µg/g
(ppm). Additionally, by moving
higher concentration elements into
higher resolutions, a further ~ 50-
fold increase in measurable concentration can be achieved [82].
4. Separation and pre-concentration methods
4.1. Possible on-line separation of actinides Besides the off-line actinide separation by using convenient extraction or ion chromatography,
the possible on-line separation was recently established in several analytical labs [83-85] for
separation of long-lived radionuclides with e.g. High Performance Liquid Chromatography
17
(HPLC), Capillary Electrophoresis (CE), etc. For, instance, Perna et al. [86] studied the
application of HPLC in the combination with mixed Dionex CS5A and CG5A columns for on-
line chromatography determination of lanthanides and actinides in the nuclear fuel samples. The
limits of detection obtained in these experiments were 0.25 ng ml-1 and 0.45 ng ml-1 for
lanthanides and actinides, respectively.
In the present study, the relevance of using CE for separation of lanthanides was explored. The
results of the measurements (see Fig. 4.1) yielded the limit of detection for lanthanide
determination in the range of 0.005 – 0.05 ng ml-1. The main factor, that affected the LODs for
lanthanides in developed method, was the small volume of the sample (about 30 nl), that was
injected into ICP-MS.
Fig. 4.1. Chromatogram of CE separation of 100 ng ml-1 of lanthanides in systemically prepared standard solution
measured by ICP-SFMS “Element”.
0
500000
1000000
1500000
2000000
2500000
3000000
3500000
4000000
4500000
300 350 400 450 500 550
Time, s
Ion
inte
nsity
, s
La
Ce
Eu
Tb
Gd
Sm Ho Er
Tm Nd Dy Yb Lu
Because the main scope of the PhD thesis was to develop the methods permitting the ultratrace
determination of long lived radionuclides, the off-line separation and co-precipitation methods
were investigated for the separation and /or pre-concentration of radionuclides of interest.
18
4.2. Off-line actinide separation by means of extraction chromatography
The extraction chromatography combines the selectivity and the flexibility of a conventional
technique as the liquid-liquid extraction with the versatility and the simplicity of a
chromatographic column. In this kind of chromatography, the stationary phase consists of an
organic complexant that is supported by a porous substrate. The solute retention proceeds from its
tendency to form stable complexes with the organic compound sorbed on the surface of the
substrate. The solute distribution coefficients are often derived, with good results, from the
existing data of equivalent systems of liquid-liquid extraction[87]. In the scope of present study,
the two extraction chromatography resins (Eichrom’s UTEVA and TEVA-Spec resins) for
separation and pre-concentration of actinides prior to their ICP-MS determination were tested.
4.2.1. UTEVA resin
The UTEVA – Spec [Uranium and Tetravalent Actinide Specific] (Eichrom Industries, USA) is a
extraction chromatography resin, that enable one to separate and concentration uranium and
tetravalent actinides from aqueous solution. The extractant in the UTEVA Resin, diamyl,
amylphosphonate (DAAP) forms nitrato complexes with the actinide elements. The formation of
these complexes is driven by the concentration of nitrate in the sample solution. Therefore, the
uptake of the actinides increases with increasing nitric acid concentration[88]. The uptake of
tetravalent and hexavalent actinides is similar and the sorbed actinides can be eluted from the
resin with dilute nitric acid. The addition of a complexant agent to the acid solution drastically
reduced the capacity factors of the actinide ions. The effect of some complexant agents on the
actinide capacity factor is described by Horwitz et al. [88]. Most of the mono-, di- and trivalent
metal ions (e.g. Li, Al, Ca, Am, Cm) are not retained when the concentration of the nitric acid is
lower than 6M [88].
The UTEVA resin has been applied to the variety of analysis: uranium measurements in
environmental samples [89], sequentional determination of uranium with plutonium [90], clean-
up of uranium content in sample prior to analysis of other elements [91], measurements of
actinides in urine [92] and in high level waste [93]
19
In this study the use of UTEVA resin for separation of U from the high salt matrix of different
samples was studied.
4.2.2. TEVA resin
The active component of the TEVA resin is and aliphatic quaternary amine. As such, it has
properties similar to those of typical strong anion exchange resins. However, because the
functional groups are in a liquid form, rather than fixed to a polymer backbone, these groups have
greater mobility to coordinate around target anions. This means that the uptake of these ions is
generally higher at much low acid concentration [94]. TEVA resin provides a simple and
effective method for the separation and pre-concentration of tetravalent actinides form aqueous
solution. Tetravalent plutonium and neptunium are efficiently sorbed from a wide range of nitric
and hydrochloric acid concentration [95]. Similarly, thorium is strongly sorbed from nitric acid
solution. Under the same condition, many commonly encountered cations as alkali, alkaline
earths, transition metals and fission products are essentially not retained by the resin. The
complete behaviour of actinide ions in nitric and hydrochloric media has been described by
Horwitz et al [96].
TEVA resin has been exploited in many labs worldwide for separation of tetravalent
actinides [62, 97], technetium analysis [98] or to separation of trivalent actinides from
lanthanides [99]
In the present Ph.D. thesis TEVA resin was mainly applied for separation and pre-concentration
of Pu from the sample matrix as well as uranium.
4.3. Pre-concentration methods
The actinide elements are normally released into the environment at very low concentration level.
Due to their high toxicity it is very important to develop analytical procedure able to pre-
concentrate them from the matrix and reach the lower detection limit. Several methods based on
ion chromatography [100], liquid-liquid extraction [101], selective precipitation [102], extraction
chromatography [103, 104] have been reported in the literature. For instance, Muramatsu et. al.
20
[87] investigated 239Pu and 240Pu in environmental samples using Dowex 1X8 and Eichrom’s
TEVA chromatographic resins for the separation and pre-concentration of Pu. The successful 10-
to 50-fold pre-concentration as well as purification of Pu was typically observed. However, in the
samples such as urine, sea water etc, where concentration of selected radionuclides (e.g Pu, Am,
etc) is very low, further enrichment of these transuranium element is required for accurate
analysis. For this purpose, a combination of co-precipitation with extraction chromatography
separation has been successfully established in order to concentrate and separate analyte prior to
analysis by α-spectrometry [32, 102, 105] or by ICP-MS [106].
Different types of selective co-precipitations (e.g. on Ca(PO4)2, MnO2, Fe(OH)3 etc) followed
with further analyte extraction chromatography have been investigated in this study for pre-
concentration of long-lived radionuclides and their determination in ultra-trace concentration
level.
21
5. Laser ablation inductively coupled plasma mass spectrometry
5.1. Basics and instrumentation of LA-ICP-MS
To an increasing extent LA-ICP-MS is the method of choice for the direct analysis of solid
samples with respect to the long lived radionuclides determination in variety of samples type [3,
107, 108]. Since their development and first application in 1985 [71, 109] the This powerful
analytical technique underwent a unique development in trace ultratrace and isotope analysis.
Significant improvements in LA-ICP-MS have been achieved due to the rapid development in
laser technology. In the past 20 years, almost all available laser wavelengths, have been tested in
combination with ICPMS, however the most widely usage the UV wavelength (266, 213 and193
nm) have been found [110]. This in turns demonstrates the advantages of shorter wavelengths in
the ablation behavior.
For the direct analysis of solid samples in material science by LA-ICP-MS, the evaporation of
sample material by a focused laser beam is achieved mostly in an inert gas atmosphere (mostly
Ar) under normal pressure. The ablated sample material is transported with the argon gas stream
into an ICP, where the atom ionization takes place. Positively charged ions then analyzed using
different types of mass spectrometers for analyzing.
The advantages of LA-ICP-MS are
• Direct analysis of solid materials, particularly for dissolution-resistant minerals.
• Minimum sample preparation.
• Reduced reagent and labor costs.
• Providing spatial information by allowing analysis of small selected areas.
• Avoiding solvent induced spectral interferences.
• Avoiding volatile element loss (e.g. As and Se).
• Avoiding dilution errors and sample transfer losses arising from sample handling
steps.
22
5.2. Application of LA-ICP-MS for determination of long lived
radionuclides
At present the determination of long lived radionuclides by LA-ICP-MS is increasingly
applied worldwide [64]. In comparison to ICP-MS for solution analysis, time consuming
sample preparation steps can be avoided with this solid analytical technique, and the risk
of contamination can be reduced significantly. This is of great importance, particularly for
the analysis of high purity materials. In addition, LA-ICP-MS шs capable of rapidly
determining the element composition of major, minor and trace element of unknown
samples. Furthermore, a major advantage of LA-ICP-MS is the possibility of performing
spatially resolved analysis, which is of interest for the survey analysis on inhomogeneities
(solid or fluid inclusions) in many materials.
At present the applications of LA-ICP-MS are described as with respect to the analysis of
the naturally occurring radioactive elements (e.g U, Th) as in characterization of the
artificial radionuclides in different samples. For instance, Boulyga et al. [31] studied Pu
isotope ratios and americium in moss samples which were collected from the eastern
Italian Alps (1500 m a.s.l.). The frozen samples were cut into 1-2 cm section and
analyzed separately to obtain the distribution curves of vertical concentration. For
plutonium and americium isotope analysis 1-2 g of the samples were ached, leached,
separated and electrodeposited on a stainless steel disk with respect to analytes and
analyzed by alpha spectrometry and LA-ICP-MS. The limits of detection of selected
radionuclides in moss sample at 10-15 g g-1 concentration level were found and were better
compared to those of alpha spectrometry. The measured 240Pu/239Pu isotope ratio of about
of 0.212±0.003 indicated, that probable Pu contamination source was global fallout after
nuclear weapons test in the sixties. The other authors [111] studied the U-Th-Pb ratio in
the monazite samples. Based on the determined ratio the age of monazites that are as
young as several tens of million years to a precision better than 2%, was determined
In present Ph.D. study the application of LA-ICP-MS for determination of long lived
radionuclides in different types of biological samples as well as in separated proteins was
explored.
23
6. Experimental part
6.1. Instrumentation
6.1.1. Optimization and experimental parameters of double focusing ICP-MS
(ICP-SFMS)
The all measurements during the current Ph.D. study were preformed on double focusing
inductively coupled plasma mass spectrometer (“Element”, ThermoElectron, Bremen, Germany).
A grounded platinum electrode GuardElectrode2 (GE) from ThermoElectron, was inserted
between the quartz ICP torch and rf load coil in order to cool down “hot ions” in the ICP
interface and improve the sensitivity of the instrument [5]. The argon with the purity of 99.999 %
was used as a plasma gas. As the sample introduction system, mostly, the Micromist (Glass
Expansion, Romainmotier, Switzerland) and PFA-100 (CETAC, Technologies, Inc., Omaha,
NE, USA) nebulizers were applied. Aqueous solutions were introduced in the continuous flow
mode using a peristaltic pump (Perimax 12, Spetec GmbH, Erding, Germany).
Table 6.1.Optimized experimental conditions for ultratrace determination of selected actinides as well as 90Sr by
double-focusing ICP-SFMS Actinide measurements 90Sr measurements
RF power, W 1200- 1250 650 Solution uptake rate, ml⋅min-1 0.30 0.30 Cooling gas flow rate, l⋅min-1 18 16
Auxiliary gas flow rate, l⋅min-1 1.45 1.5 Nebulizer gas flow rate, l⋅min-1 0.985-1.0 1.2
Focus lens potential, V -850 -1100 Sampler cone Nickel, 1.1 mm orifice diameter Skimmer cone Nickel, 0.9 mm orifice diameter
Mass window, % 20-100 60 Monitored m/z, u 226 - 242 88, 89, 90
Runs 5-500 700 Passes 1-1000 1-5
Scanning mode Peak hopping Mass resolution, m/Δm 300, 4400 4400
24
Before the measurements the all experimental parameters were tuned in respect to the maximum
ion intensity of the analyte and the minimum background signal on the selected mass-to-charge
ratio using available standard reference materials. The optimized experimental parameters of
ICP-SFMS for the determination of long lived radionuclides and 90Sr at ultratrace concentration
level are summarized in table 6.1
Correction of mass discrimination in ICP is one of the requirements for precise and accurate
isotope ratio measurements [64, 112]. In ICP-MS the mass discrimination is a result of space
charge effects. After the ions, formed in the inductively coupled plasma, leave the skimmer cone,
the Coulomb repulsion of positively charged ions results in a loss of transmission through the ion
optical lens system, and the light ions are deflected more than the heavy ones. Therefore in ICP-
MS the measured isotope ratio of lighter to heavier isotope is smaller than the true value (e.g., 235U/238Umeasured < 235U/ 238Utrue).
The mass discrimination correction factor, assuming an exponential correction, was determined
using a 5-10 ng ml-1 NIST U500 standard solution. For calculation an equation 6.1 was applied.
exp*εmRR
meas
true Δ= , (6.1)
• where Rtrue/Rmeas - is the certified-to-measured isotopic ratio (Ri - 235U/238U), Δm - mass
difference between the isotopes of interest, εexp - mass discrimination per mass unit
The mass discrimination factor of the ICP-SFMS was always measured during each of
experiments, and further used for correction of measured intensities.
Dead time detector is of great importance for accurate measurements of isotope ratios [19], that
affects the detector systems to record fewer counts than actually occur. After an ion generates an
electron pulse at the conversion dynode, and subsequently an electron pulse in a multiplier, there
is a finite time during which the system is incapable of recording another event. The system is
effectively “dead” (i.e. unable to process another event) in this interval and, therefore, a
correction should be applied to all ion count rates (counting detection mode) to compensate for
this dead time (see Equation 6.2)
deadmeas
meascorr I
II
τ⋅−=
1 (6.2)
25
• where, and are the corrected measured ion intensities, respectively, corrI measI deadτ is the
dead time value.
Determination of the dead time of the ion detector on the utilized ICP-SFMS was performed as
follows. 235U/238U isotopic ratios in the natural uranium standard solution at the concentration of
0.4, 0.6, 08 and 1 ng ml-1 were measured, under the disable of “dead time correction” function of
ICP-SFMS instrument (see fig 6.1).
Fig 6.1. Dependence of 235U/238U isotopic ratios on the uranium concentration measured under disable “dead dime
correction” function of ICP-SFMS.
y = 0.000357x + 0.007222
0.00700
0.00710
0.00720
0.00730
0.00740
0.00750
0.00760
0.00770
0.00780
0.00790
0.00800
0.0 ppb 0.2 ppb 0.4 ppb 0.6 ppb 0.8 ppb 1.0 ppb 1.2 ppb
concentration, ppb
235 U
/238 U
isot
opic
ratio no deadtime correction
Than, in accordance to (6.3) the simulation of τ vs. 235U/238U isotopic ratios was performed in
order to achieve the smallest slope of determined dependence (see Fig. 6.2). Obtained in such
way value of dead time detector was further used by ICP-SFMS for correction of measured
intensities.
26
Fig 6.2. Dependence of 235U/238U isotopic ratios on the uranium concentration measured with the corrected dead
time of the ion detector of ICP-SFMS.
y = -0.000003x + 0.007219
0.00700
0.00710
0.00720
0.00730
0.00740
0.00750
0.00760
0.00770
0.00780
0.00790
0.00800
0.0 ppb 0.2 ppb 0.4 ppb 0.6 ppb 0.8 ppb 1.0 ppb 1.2 ppb
concentration, ppb
235 U
/238 U
isot
opic
ratio
deadtime of 16 ns corrected
Typically, detector dead time of utilized ICP-SFMS was checked periodically, e.g. 1-2 per
month, and was the range of 15-25 sec.
6.1.2. Advanced solution introduction systems (Aridus, USN, DIHEN, nano-FI-
ICP-MS)
In recent years, much effort has been devoted to the development of new, more efficient aerosol-
generation systems that can be very advantageous for improving the ICP-MS figures of merits. In
addition, to suppress oxide and hydride formation some nebulizers are equipped with so-called
desolvation systems.
Two types of nebulizer with the desolvation systems were tested: microconcentric nebulizer
(MCN) equipped with membrane desolvation system (Aridus, CETAC Technologies, Inc.,
Omaha, NE, USA); and ultrasonic nebulizer with a membrane desolvation system (USN U-
6000AT+, CETAC Technologies, Inc).
Decreasing of the sample size, required for the ICP-MS analysis of long lived radionuclide is of
special importance [3] for the purpose to reduce the radioactivity of the sample analyzed, the
27
waste, contamination of instrument tolls and dose to the operator the unique nebulizers (with the
analyte transport efficiency of 100%) such as direct injection high-efficiency nebulizer (DIHEN,
J.E. Meinhard Associates, USA) and Microflow total consumption nebulizer DS-5 (CETAC,
Omaha, NE, developed by Schaumlöffel et al. [70]) were used for solution introduction into ICP.
The DS-5 nebulizer was applied for the Flow Injection ICP-MS measurements (see Fig. 6.3) of
uranium and plutonium in extremely small sample size (~50 nL).
Fig 6.3. Experimental setup of nano-volume flow injection ICP-SFMS system
The nebulizer was fitted in a low-dead volume (8 cm3) single pass spray chamber and was
operated at low and constant carrier flow rate of 7 µL min-1, provided by a high-precision syringe
pump (CMA-100, Carnegie Medicine, Solna, Sweden). Nano-volume flow injection was
achieved by an ultra-low dead volume nano-injection valve CN-2 (Valco Instruments, Houston,
TX). The sample loop was an 8 cm long and 20 µm i.d. fused silica capillary with an internal
volume of 25 nL. Taking into account the internal port-to-port volume of the valve of 29 nL
specified by the valve manufacturer, the total sample volume was 54 nL.
28
6.1.3. Laser ablation ICP-MS
6.1.3.1. Experimental parameters of LA-ICP-MS
A laser ablation system from Bioptic (Ablascop, Bioptic laser system, Berlin) coupled to the
double-focusing sector field ICP-MS (ELEMENT, Finnigan MAT) was used as a solid sample
introduction system for the direct determination of selected radionuclides in analyzed biological
tissues, single protein, separated by 2D gel electrophoresis well as on the surface of a biological
sample (flower leaf). The schematic of such LA-ICP-MS experimental arrangement is shown on
Fig. 6.4.
Fig. 6.4. Schematic for experimental arrangement of LA-ICP-MS with cooled laser ablation chamber
CCD camera
DS-5 Calibrated solutions
Ar
The laser ablation of the analyzer material was performed with the UV wavelength of a Nd-YAG
laser (5th harmonic, 213 nm at pulse duration of 5 ns, repetition frequency of 20 Hz, laser power
density of 109 W/cm2). With this arrangement it is possible to obtain a diameter of the laser crater
in the range of 5 to 50 μm. The two different scanning procedures mostly were applied for
scanning of the sample – single spot scan (50-400 laser shots per spot) and the line scan rastering.
The ablated material was transported by argon as carrier gas into the ICP.
For calibration and optimization of ICP-SFMS a single gas flow solution- based calibration was
procedure was applied using an USN or direct coupled microflow total consumption DS-5
nebulizer (see Fig. 6.4). Using this arrangement, simultaneous optimization of the nebulizer gas
29
flow rate for the nebulizer and the carrier gas flow rate for the transport of laser-ablated material
into ICP is possible.
6.1.3.2. LA-ICP-MS with cooled LA-chamber
Because of the most soft biological tissues (e.g. thin sections of liver, brain, etc ) mainly consist
from the water (up to 90%), the LA-ICP-MS analysis of this samples becomes a very difficult
process[113]. In order to analyze biological matrices a cooled PFA laser ablation chamber, was
developed in present study (see Fig 6.4). The cooling system of the ablation chamber is arranged
using two Peltier elements in serial connection under the target holder made of aluminum. Using
this setup at the current and voltage of 0.6 A and 16 V, respectively, applied to the Peltier
elements, a temperature of the target holder in the LA chamber of about -15ºC was observed.
6.2. Quantification and evaluation of analytical data
For data quantification and evaluation, generally, following calibration strategies were applied:
external calibration, standard addition and isotope dilution method. For quantification of LA-ICP-
MS measurements solution based calibration was used.
6.2.1. External calibration using standards reference materials
Because the response of the mass spectrometer in counts per second is directly proportional to the
concentration of a given element in a sample, it is relatively easy to calibrate the system using the
external standards of differing concentrations. Any sample entered into the mass spectrometer
under exactly the same conditions will return a count rate, which can be converted directly to
concentration for each element from a calibration curve. Typical calibration curve for uranium
determination by ICP-SFMS with the correlation coefficient of R2=0.9999 is shown on the Fig
6.5.
30
However due to the possible altering of the sample introduction condition (e.g. variation in
plasma ionization efficiency, clogging effect, difference in matrix or concentration of the sample
etc [48, 101]) between sample and standard reference material the accurate analysis of the
samples by ICP-MS becomes sometimes difficult or even impossible. In order to minimize these
effects, internal standard element is usually added to all samples and standards measured.
In the present study In was typically used for this purpose (see Fig 6.5).
Fig. 6.5. Calibration curve for uranium measured by ICP-SFMS. (1 ng ml-1 of In was used as internal standard).
0
1000000
2000000
3000000
4000000
5000000
0 0.5 1 1.5 2 2.5U concentration, ppb
U io
n in
tens
ity, c
ps
0
400000
800000
1200000
1600000
2000000
In io
n in
tens
ity, c
ps
U-238 In-115
R2= 0.9999
R2= 0.9999
6.2.2. Standard addition method
Standard addition technique is used for the multielement analysis of the sample, with relatively
complex matrices or when the suitable blank solution is not available (e.g measurements in urine,
tissues, etc). Standard addition calibration provides an effective way to minimise sample-specific
matrix effects through the use of sample solutions that have been "spiked" with a known
concentration of each analyte element.
31
R2 = 0.9985
-10000
0
10000
20000
30000
40000
50000
-5 0 5 10 15 20 25
U concentration, ppb
U io
n in
tens
ity, c
psU-238Linear (U-238)
Fig 6.6. Dependence of uranium ion intensity in urine sample on added the U(nat) spike concentration.
From the obtained calibration curve the concentration of measured element can be found (see Fig
6.6.) by the interception of the regression line with the abscissa axis.
6.2.3. Isotope dilution analysis
Isotope dilution analysis (IDA) is an excellent and important quantification technique in mass
spectrometry for accurate trace element determination. In IDA one or two highly enriched isotope
tracers or ‘‘spikes’’ of the element to be determined with well-known concentrations are added to
the sample (mixed and well homogenized with solid sample or aqueous solution). The trace
element concentration was found by measuring changed isotope ratios in the sample-spike
mixture (X) compared to those in sample (S) and highly enriched isotope tracer (T) using the eqn.
6.1.:
QS=QT × (T-X) / (X-S) × mS/mT (6.3)
where QS is the element concentration in the sample; QT is the element concentration in the
highly enriched tracer, T is the isotope ratio of two selected isotopes in the highly enriched tracer;
S is the isotope ratio of these two selected isotopes in the sample; X is the measured isotope ratio
of the two selected isotopes in the mixture; and mS and mT are the atomic mass of the element in
32
nature and of the isotopic enriched element, respectively. IDA is applicable to all elements with
at least two stable isotopes or long-lived radionuclides.
6.2.4. Solution based calibration in LA-ICP-MS
Solution based calibration can be applied in LA-ICP-MS for an easy and rapid quantification
procedure [114]. By this means the nebulizer gas flow coming from nebulizer is used as the
carrier gas flow for the laser ablation process. In order to achieve matrix matching the standard
solution were nebulized and simultaneously a suitable blank target was ablated with a focused
laser beam[114]. In the present work for the mass spectrometric measurements an ultrasonic
nebulizer (U-6000AT) or DS-5 nebulizers were directly coupled to laser ablation cell (see Fig.
6.4).
6.3. Samples preparation
Before the ICP-MS measurements the analyzed samples were subjected to the sample preparation
procedures in order to concentrate or/and separate the analyte atoms from the sample matrix.
Different pre-concentration and separation procedure were tested.
6.3.1. Pre-concentration of actinides
6.3.1.1. Co-precipitation of actinides with MnO2 and Fe(OH)3 from large volumes
of water samples
About 100 L of the water sample (e.g. water from Sea of Galilee) was collected in containers
previously washed repeatedly with 2% v/v nitric acid in 18 MΩ cm-1 water. A schematic diagram
of the sample preparation procedure e.g. for Pu co-precipitation is shown in Fig 6.7.
33
The 100 L water sample was acidified with nitric acid to pH = 2. In order to determine the
recovery of the method the sample was spiked with 2.1 pg of 242Pu and thoroughly mixed. Then
35 mL of KMnO4 (~2.1g) was added. All Pu in this step was oxidized to the Pu6+ oxidation form.
The solution was adjusted to pH = 8-9 with NaOH and 0.5M MnCl2 (2 x vol. of KMnO4) was
added in order to precipitate MnO2. Ultratraces of Pu are co-precipitated together with MnO2.
After settling of MnO2 overnight with co-precipitated Pu it was filtered by gravity over the filter
paper and dissolved in 2 L of 2M HCl+30 ml NH2OH⋅HCl (0.1g/ml).
To the dissolved filtrate 50 mg of Fe3+ as FeCl3 was added and solution was neutralized with 2M
NaOH. In order to reduce Fe3+ to Fe2+ and Pu6+ to Pu3+ ~2ml NH2OH⋅HCl was added. After that,
Pu3+ was oxidized with 20ml NaNO2 (0.1g/ml) to Pu4+, since tetravalent Pu is most favorable for
separation on TEVA resin. The solution was adjusted to pH = 8-9 with 2M NH4OH and heated
for ~2 hours (60-70ºC) to improve coagulation of the Fe(OH)3 with co-precipitated Pu. After that,
the precipitate was settled, transferred to a centrifuge tube and centrifuged for approximately 10
minutes at 4000 rpm. Supernatant was decanted and discarded to waste; the precipitate was
dissolved with 11.2 mL 7M HNO3 + 4 ml 0.5M Al(NO3)3 and diluted with MilliQ water up to a
volume of ~25 mL so that 3M HNO3 solution was obtained.
6.3.1.2.Co-precipitation of plutonium with Ca(PO3)2 from urine samples
Analytical method for ultratrace Pu determination in urine samples was developed. The urine
sample was collected from healthy adult volunteers in containers previously washed repeatedly
with 2% v/v nitric acid in 18 MΩ cm water. A schematic diagram of the sample preparation
procedure is shown in Fig 6.8.
The 1 liter of fresh urine was acidified with nitric acid to pH 2. In order to determine the recovery
procedure the urine was spiked with 4 pg of 242Pu and thoroughly mixed. 0.5mL of 1.25 M
Ca(NO3)2 and 0.2mL of 3.2 M (NH4)2HPO4 was added and the urine was heated to a temperature
of approximately 40-50°C. After that concentrated NH4OH was added (very slowly) up to the
point where the formation of Ca3(PO4)2 precipitate was observed. The sample was then stirred
with a glass rod, heated for 20 min and allowed to settle overnight. After settling the precipitate
was transferred to a centrifuge tube and centrifuged for approximately 10 minutes at 4000 rpm.
The supernatant was decanted and discarded to waste; the precipitate was filtered by gravity over
the filter paper.
34
Fig 6.7. Sample preparation procedure of co-precipitation and separation of Pu from large volume water
samples
35
100 L water sample spiked with 2.125pg 242Pu
Fe(OH3) - co-precipitation
Separation of Pu on TEVA resin
Send sample through the column
Add 50 mg Fe3+ as FeCl3
Add 2M NaOH to decrease acid conc.
Add ~2ml NH2OH⋅HCl
Add 20 mL NaNO2 (0.1g/mL)
Adjust to pH 8-9 with 2M NH4OH
Centrifugation 10 min at 4000 rpm,
Filter precipitate and dissolve in 11.2 mL 7M HNO3+4 ml 0.5M Al(NO3)3
Dilute with MilliQ up to 25 ml
Place 0.5g TEVA in the cartridge, condition with 5 ml 3M HNO3
Wash with 3×10mL 3M HNO3
Elution Pu 15 mL 0.05M HF+ 0.05M HNO3
MnO2 - co-precipitation
Add 35mL KMnO4 (~2.1g)
Adjust pH to 8-9 with NaOH
Add 0.5M MnCl2 (2x vol. KMnO4)
Re-adjust to pH 8-9
Stir and settle overnight; filter precipitate
Dissolve in 2 L 2M HCl+30 ml NH2OH⋅HCl
Alow Fe(OH)3 precipitate to settle
ICP-MS measurements of Pu
Fig 6.8. Sample preparation procedure for Pu analysis in urine.
1L urine spiked with 4ng 242Pu
Ca3(PO4)2 - co-precipitation
Separation of Pu on TEVA resin
Add 0.2 g of TEVA resin
Send sample through the column
Add 0.5mL of 1.25 M Ca(NO3)2
Add 0.2mL of 3.2 M (NH4)2HPO4
Heat 40-50ºC
Add NH4OH to precipitate Ca3(PO4)2
Stir and settle overnight
Centrifugation 10 min at 4000 rpm,
Filter precipitate
Dissolve in 25 mL of 3M HNO3
Add 1 mL 3M NaNO2 + 4 ml 0.5M Al (NO3)3
Shake 120 min 300 min-1
Wash 3×10mL 3M HNO3
Elution Pu 15 mL 0.05M HF+ 0.05M HNO3
Evaporation to 10 ml
PFA 100-ICP-SFMS measurement of Pu
Evaporate to 0.5 mL
DIHEN-ICP-SFMS measurement of Pu
5 mL 5 mL
36
6.3.1.3. Co-precipitation on crown ether resins
Besides the separation of actinides from the sample matrix by using crown resins, successful co-
precipitation of the analyte on the have been performed. Depending on the method used, pre-
concentration factor in the range of 5 to 10 was achieved.
6.3.2. Samples separation from complex matrices
To avoid matrix effect as well as to purify analyte atoms from the interfering ones actinide were
separated by means of extraction chromatography. Different types of crown resin with the
different protocols developed were tested for this purpose.
6.3.2.1. Extraction chromatography protocols
6.3.2.1.1. Actinide separation on TEVA-resin
Eichrom's TEVA resin (Darien, Illinois, USA) [particle size 50-100μm, active component:
aliphatic quaternary amine] has been used as a stationary phase, manly, for Pu separation ether
from sample matrix or from precipitate carrier (e.g . Fe(OH)3). Schematic protocol of Pu
separation on TEVA-resin is shown in Figs 6.7, 6.8.
0.5 g of TEVA resin was placed into the appropriate cartridge tubes and preconditioned
with 5 mL 3M HNO3. After that the sample solution was loaded with the resin and rinsed
with 3×10 mL 3M HNO3. Then plutonium was eluted with 3×5mL 0.05M HF +
0.05M HNO3 into a Teflon beaker. Because of high concentration of U in the separated
sample (U concentration after first separation was, usually, about 0.5 ng mL-1), Pu was
separated on the TEVA resin for a second time. After the first separation the Pu fraction
was evaporated to dryness and the residue was dissolved with 11.2 ml of 7M HNO3. Then
4 ml of 0.5M Al(NO3)3 was added and the sample solution was made up to 25 ml with
H2O and then subjected to the same TEVA separation protocol as described above. The
Pu concentration and the Pu isotope ratio were then measured by ICP-SFMS.
37
6.3.2.1.2. Actinide separation on UTEVA-resin
Eichrom's UTEVA resin [particle size 50-100μm, active component: diamyl, amylphosphonate]
has been used as a stationary phase for U separation. 2 g of UTEVA resin (see Fig 6.9) was
placed into the appropriate cartridge tubes and preconditioned with 10 mL 1M HCl. Then that the
sample solution was loaded with the resin and rinsed with 3×5 mL 3M HNO3. The UTEVA resin
was converted to chloride system with 5 ml 9M HCl. After that uranium was eluted with 20 ml
1M HCl into a Teflon beaker. The uranium concentration and the uranium isotope ratio were then
measured by ICP-SFMS.
Fig 6.9. Extraction chromatography protocol of U separation on Eichrom’s UTEVA resin
Sample (urine, water etc) Spiked with 2 pg of 233U
Precondition of UTEVA resin with 10 ml 1M HCl
Load sample throuph column
Wash column wiht 3×5ml 3M HNO3
Elut uranium with 15 ml 0.05M HF+ 0.05M HNO3
Uranium ICP-SFMS measurements
Convert to chloride system with 5ml 9M HCl
6.3.2.1.3. Separation of Sr on “Sr-specific” resin
Sr-spec resin [active component: octanol solution of 4,4’(5’)-bis(t-butylcyclohexano)-18-crown-6
sorbed on an inert polymeric support] was applied for separation of Sr from sample matrix in
water as well as urine samples. The resin was obtained as pre-packaged 2 mL columns from
Eichrom Industries. Note, the uptake of Sr by this resin increases with increasing nitric acid
concentration. At 8 M nitric acid, k’ is approximately 90 and it falls to less than 1 at
concentrations of nitric acid less than 0.5 M. After co-precipitation of Sr with Ca(NO3)2, the
38
residue was dissolved in 10 mL of 8M HNO3 and passed through the Sr column. Prior to this,
columns were washed with 25 ml of 0.05M HNO3 to elute residual Sr from the resin. A vacuum
manifold was used to facilitate the passage of the sample through the resin. The strontium
remained on the resin of the column and was then eluted with a 5 mL volume of 0.05 M HNO3
into appropriate tube and the solution was further used for ICP-SFMS measurements.
6.3.2.1.4. Ra separation on “Ra specific” disk
Laboratory prepared “Ra-specific” disk was used for Ra purification in the mineral and ground
water samples (see Fig.6.10). The disk was prepared as follows. A cellulose-nitrate filter,
previously washed with distilled water, was immersed in ~1w/w% of KMnO4 in MilliQ water at
50ºC for 60-70 min. Then the filter was thoroughly washed with distilled water.
200 ml of analyzed water samples were acidified to pH 6 with concentrated HNO3. The prepared
"MnO2 filter" was placed into the apparatus for filtering and sample was loaded at ~ 1ml min-1
(gravity flow). After that, the filter was rinsed with MilliQ water and placed into the 15ml tubes
for leaching with 1M HNO3 (~13ml) in an ultrasonic bath for 1h. Leached sample was filtered
twice through the small Teflon filter and acidified with concentrated nitric acid to molarity of
about 3. Then the sample (final volume ~15ml) was used for further separation of Ra (manly
from residual Sr) on the Eichrom “Sr-specific” resin, as described above.
6.3.3. Sample preparation procedure for ICP-SFMS measurements of urine
samples
Microwave digestion procedure has been developed in order to decompose analyzed urine
samples prior to ICP-SFMS determination of long lived radionuclides. The urine sample of 1 ml
volume were digested in small, cleaned 10 ml Teflon® vessels (XP-1500) in a microwave oven
(Mars-5, CEM, Microwave Technology Ltd., Matthews, N.C., USA) with 1 ml of 65% HNO3
and 0.5 ml of H2O2. The optimized digestion program includes heating for 10 min at 150 W,
co0lling for 2 min (0 W), and digestion for 10 min at 300 W. After that the samples were diluted
with deionized MilliQ water up to 10 ml and acidified to 2% subboiled HNO3. The diluted
samples were used for ICP-SFMS determination of selected long-lived radionuclides.
39
Fig.6.10. Sample preparation protocol for separation and preconcentration of radium in mineral or in ground water
samples
0.2l mineral water sample adjust pH sample to 6 with HNO3
Pre-concentration of 226Ra on “MnO2 filter”
Separation of 226Ra on Eichrom’s “Sr-specific resin”
Rinse with 3 ml of 3M HNO3
Wash resin with 25 ml 0.05 M HNO3
Immerse cellulose-nitrate filter in ~1w/w% of KMnO4 in MilliQ at 50ºC for 60-70 min
Wash filter thoroughly, place into apparatus for filtering
Send sample through the filter at 1 ml min-1 (gravity flow)
Place the filter into 15 ml tube
Filter the sample with Teflon filter
Leach with 1 M HNO3(~13 ml) in ultrasonic bath for 1h
Set molarity of sample to 3 with HNO3
Dilute the “sample + rinsing solution” to 20 ml with MilliQ water
Wash resin with 10 ml 8M HNO3
Conditionize with 3 ml of 3M HNO3
Send the sample through the resin
ICP-SFMS measurements of 226Ra concentration
40
6.4. Isotopes standards, standard reference materials and chemicals
Single-element standard stock solutions natural occurred radionuclides (e.g. Th, U) were obtained
from Merck (Darmstadt, Germany) and were used for determination of concentration of isotope
of interest. 242Pu isotopic standard (NIST SRM 4334F, National Institute of Standards and
Technology, USA) was applied for determination of Pu concentration in analyzed samples as
well as to control recovery of the developed procedure.
NIST standard reference materials U005, U350 and U930 and solutions of uranium CCLU-500
(Laboratory Standard, Nuclear Research Center, Prague, Czech Republic[115]) were used for the
optimization and evaluation of the developed methods for isotope ratio measurement of uranium.
Uranium isotope ratios for the CCLU-500 standard have been established (by calibration against
the NIST-500 SRM using TIMS[5]. Isotopic standard reference material NIST U020 was applied
for determination of mass discrimination factor. The values of uranium isotopic ratios in applied
standard reference materials are summarized in Table 6.2.
For the determination of the precision and accuracy of 240Pu/239Pu isotope ratio measurements
synthetically prepared aqueous laboratory standard solution with known plutonium isotopic ratio
composition (240Pu/239Pu=0.2960±0.0026, n=10) was used.
The all solutions were diluted to the necessary concentration with high purity deionized water
(18 MΩ), obtained from a Millipore Milli-Q-Plus water purifier (Millipore Bedford, MA, USA).
For the experiments with improvement of LOD for 236U the samples were diluted with deuterium
oxide (obtained from Merck, purity 99.95%). The solutions were always acidified to 2% HNO3
with sub-boiled nitric acid. In case of dilution with D2O, final purity of deuterium after adding
the standards and acidifying was ~99.90%.
For calibration of LA-ICP-MS measurements of thin soft tissues (brain samples), matrix-matched
laboratory standards with well-defined element concentrations were prepared. The procedure of
preparation of matrix-matched synthetic laboratory standards is shown in Figure 6.11. Three
laboratory synthetic standard solutions containing the elements of interest (Cu, Zn, U and Th) in
defined concentrations were prepared.
41
Table 6.2. Standard isotopic ratios of U in applied Standard reference materials
234U/238U 235U/238U 236U/238U
NIST U005 0.0000219 0.0049194 0.0000468
NIST U020 0.0001276 0.0208100 0.0001684
NIST U350 0.0038790 0.5464880 0.0025980
NIST U500 0.0104220 0.9996980 0.0015190
CCLU-500 0.011122 0.99991 0.002789
NIST U930 0.2009670 17.3486980 0.0376770
Three slices of the same brain tissue (each about 0.65 g) were spiked with selected standard
solutions. The final concentrations in brain tissue are 10, 5, 1 µg g-1 of Cu and Zn and 1, 0.05,
0.01 µg g-1 of Th and U. The fourth slice was not spiked and was used for blank correction. All
tissue brain samples were carefully homogenized and centrifuged at 5000 rpm for 5 min. After
that, samples were frozen at a temperature of -50ºC. Frozen matrix-matched synthetic laboratory
standards of human brain tissues from the hippocampus were cut into sections 10 μm in thickness
and placed onto the glass substrate. By using of matrix-matched synthetic laboratory standards
calibration curves has been measured in LA-ICP-MS.
Fig. 6.11. Procedure for preparation of synthetic matrix-matched laboratory standards for LA-ICP-MS measurements of selected elements in thin cross section of brain samples
Three laboratory synthetic standard solutions with elements of interest (Cu, Zn, U and Th) and well-defined concentrations were prepared
Three slices of the same brain tissue (each of about 0.65 g) were spiked with selected standard solutions (final concentration of Cu and Zn in brain tissue: 10, 5, 1 µg g-1 and of Th and U: 1 , 0.05, 0.01 µg g-1 )
The fourth slice was not spiked and was used for blank correction
Brain samples tissue were properly mixed and centrifuged at 5000 rpm for 5 min After that samples were frozen under the temperature -50ºC
Frozen brain samples were cutted with microtone in a thickness of 10 μm in the way similar to the sample done and placed onto the glass substrate
Prepared in such way standards were further used for calibration of LA-ICP-MS measurements of concentration of selected elements in brain hippocampus
42
7. Results and discussions
7.1. Methodical development for analysis of actinides by ICP-SFMS
7.1.1. Improvement of LOD for 236U and minimum 236U/238U detectible isotope ratio
The limit of detection for 236U by ICP-SFMS is constrained, mainly, by limited abundance
sensitivity of ICP-MS instruments [16, 23] as well as by isobaric interference from235U1H+ [10].
In the following paragraph methodical developments in order to improve the figures of merit for
ICP-SFMS determination of 236U are discussed.
Due to the strong peak tailing of 238U+ on mass 236 u the accurate determination of 236U/236U
isotopic ratios were not adequate at the required concentration level by utilized ICP-SFMS.
Therefore, in order to improve abundance sensitivity of ICP-SFMS for 236U measurements,
medium mass resolution mode (m/Δm=4450) was applied.
For the ICP-SFMS (ELEMENT), the abundance at mass 236 u was estimated based upon
measurements performed with a 232Th standard solution. All experimental parameters were first
optimized in respect to the maximum of 238U+ ion intensity. A 0.1 μg ml-1 Th standard solution
(232Th abundance 100%) was used to obtain a statistically “true” peak tail for studying abundance
sensitivity. This avoids measuring the combined influences of 235U+ and 238U+ at m/z 236. In
order to minimize the effect of other limiting factors, such as possible contamination of the blank
and molecular ion formation, the abundance sensitivity for the isotope with mass 232.0375 u for 232Th was studied at masses m ± 0.5, m ± 1.5, m ± 2.5 etc. This approach has the advantage that
abundance sensitivity can be measured even when isobaric interferences are presented, so the
peak tail are not affected by possible interferences at masses m ± 1 u, m ±2 u, m ± 3 u etc.
Measured in medium resolution abundance ratio sensitivity for 232Th is presented on the Fig
7.1.1. The intensity of the 232Th+ was 16 Mcps.
43
Fig. 7.1.1. Measured ratio of peak tail intensities at masses m ± xn (xn = 0.5 u, 1.5 u and 2.5 u) to peak intensity at
mass m (m = 232.0375 u for 232Th)
1.0E-07
1.1E-06
2.1E-06
3.1E-06
4.1E-06
5.1E-06
6.1E-06
7.1E-06
8.1E-06
9.1E-06
-4 -3 -2 -1 0 1 2 3 4
Mass difference
Rel
ativ
e pe
ak ta
il in
tens
ity
The abundance sensitivity for two mass units below the tailing peak in ICP-SFMS was calculated
using equation 7.1.1.
2
2
−
− =m
mm
IIAS (7.1.1),
• where ASm-2 is the abundance sensitivity for two mass units below the tailing peak in ICP-
SFMS, Im and Im+2 are the ion intensities at the m/z m and m-2, respectively (in present
experiment on m/z 232 u and 232 u).
Besides the peak tailing from 238U+, the abundance sensitivity of the ICP-SFMS in respect to 235U+ peak tailing on 236U was also considered. Obtained values of abundance sensitivities for
two mass units below and one mass unit up the tailing peak are summarized in Table 7.1.1, that
represents some important figures of merits of ICP-SFMS in current experiments.
44
Table 7.1.1. Figures of merit of ICP-SFMS (m/Δm=4450) for several solution introduction devices measured on the
samples diluted with MilliQ or heavy water
Abundance sensitivity Solution
uptake
rate,
ml min-1
Sensitivity of 238U,
Mcps ppm-1
Uranium
hydride
rate,
UH+/U+m
m 2− m
m 1+
LOD (3σ) for 236U
10-15g ml-1
Samples diluted with MilliQ water
Meinhard
USN with desolvator
Aridus
0.58
2.0
0.1
205
1800
400
1.05×10-4
1.20×10-5
1.00×10-5
1.06×10-6
0.98×10-6
0.98×10-6
4.9×10-6
4.8×10-6
4.8×10-6
0.41
0.16
0.13
Samples diluted with heavy water
Meinhard
USN with desolvator
Aridus
0.58
2.0
0.1
200
1770
400
6.05×10-6
1.10×10-6
9.02×10-7
1.02×10-6
0.98×10-6
0.98×10-6
4.8×10-6
4.8×10-6
4.8×10-6
0.19
0.09
0.04
The hydride formation rate of uranium (UH+/U+) was studied in ICP-SFMS using H2O and D2O
solvents. A typical ICP mass spectrum of uranium in the mass range of 237.5-241 u measured at
medium mass resolution (m/Δm = 4450) for a 0.1 μg ml-1 solution of uranium with natural
isotope composition diluted in D2O is shown in Fig. 7.1.2.
Fig 7.1.2. ICP-MS spectrum of 238U1H at mass resolution of 4450 measured for natural uranium, diluted with D2O
using Meinhard nebulizer.
45
0
100
200
300
400
500
600
700
800
900
1000
m / z
inte
nsity
, cps
238 239 240 241
238U1H+
238U2D+
238U+
Instead of UH+ at mass 239 u (that disturb e.g correct 239Pu+ measurements [116]) the formation
of UD+ ions were observed, so by using heavy water the determination of 240Pu will be disturbed.
The results of hydride formation rate UH+/U+ for different nebulizers using MilliQ and heavy
waters are summarized in Table 7.1.1. In case of MilliQ water as solvent, application of a
ultrasonic nebulizer with microporous Teflon membrane desolator allowed reducing of UH+/U+
ratio down to 1.20×10-5, comparing to 1.05×10-4 for Meinhard nebulizer (without desolvator).
The lowest hydride formation rate 1.0×10-5 was achieved with microconcentric nebulizer with
desolvator Aridus, reducing effectively the formation rate of uranium hydride ions UH+ or
possible isobaric interference of 235U1H+ on 236U+ by factor ten in comparison to Meinhard
nebulizer.
Significant reducing of hydride formation rate for Meinhard nebulizer was found when, instead
of MilliQ water, D2O was applied for dilution the samples. Obtained value of UH+/U+ ratio was
6.05×10-6, that almost two orders of magnitude lower the hydride formation ratio, achieved with
MilliQ water. The lowest formation of uranium hydride molecular ions (9.02±0.3×10-7) was
observed for microconcentric nebulizer Aridus with membrane desolvator. The decreasing of
formation ratio for nebulizers with desolvators (USN and Aridus: 10 fold and 11 fold,
respectively) is lower than for Meinhard nebulizer (17 fold) for the samples, diluted with heavy
water.
By the measurements was found (see Table 7.1.1.), that even with application of nebulizers with
desolvation system (USN or Aridus) for measurement the samples, diluted with heavy water, the
complete elimination of hydride formation is still not possible. The most probable reason for this
could be the not “100%-pure” deuterium oxide solution (in present work – 99.9%), used for
dilution samples. Moreover, formation of hydride ions is caused by hydrogen, as well as water,
which are presented as an impurity in argon and residue gas, respectively. Further study of this
effect will be of interested in order to decrease the uranium hydride formation and, therefore,
improve ability of detection of 236U.
Fig 7.1.3 presents the minimum detectable ratio (3σ) for 236U/238U isotopic ratio of uranium (see
equation 7.1.2.), for different nebulizers, using MilliQ and D2O waters for dilution of the
samples.
238 m/z onintensity 3236m/z on signal ratio isotopic UU/ detectable minimum 238236
=+=
=σ
(7.1.2)
46
Decreasing of the minimum detectable ratio about of one order of magnitude was observed for all
nebulizers. The largest effect was found with Meinhard nebulizer (because no desolvator is used)
due to significant elimination of 235U1H+ ions when heavy water for dilution is used.
Fig 7.1.3. Minimum detectable ratio criteria (3σ) for 236U/238U isotopic ratio of natural uranium for different
nebulizers using H2O and D2O for dilution of the samples (R=4450)
0.0E+00
5.0E-07
1.0E-06
1.5E-06
2.0E-06
2.5E-06
3.0E-06
3.5E-06
4.0E-06
4.5E-06
5.0E-06
Meinhard Aridus USNMin
imum
det
ecta
ble
236 U
/238 U
isot
ope
ratio
MilliQ D2O
The optimized method was further applied for measurement of 236U/238U isotopic ratio of two
natural samples, received from Israel, which were diluted with heavy water. Comparative
measurements were performed by ICP-SFMS as well as MC-ICP-MS (Nu-Instruments, UK),
installed in the analytical laboratory of Geological Survey of Israel, Jerusalem, Israel. All results
are summarized in Table 7.1.2..
Measured by ICP-SFMS 236U/238U isotopic ratio were ranged from 4.8±0.9×10-7 to 5.3±0.8×10-7
and from 6.5±1.2×10-7 to 7.4±1.5×10-7 for sample I and sample II, respectively, whereas MC-
ICP-MS measurements of 236U/238U isotopic ratio yielded 5.00±0.09×10-7 for both samples.
47
Table 7.1.2. 236U/238U isotopic ratio in natural samples, received from Israel, diluted with heavy water and measured
by ICP-SFMS using different nebulizers and by MC-ICP-MS with nebulizer Aridus.
Sample ICP-MS Nebulizer Measured 236U/238U isotopic
ratio
I ICP-SFMS Meinhard (5.3±0.8) × 10-7
Aridus (4.8±0.9) × 10-7
USN with desolvator (5.0±1.3) × 10-7
MC-ICP-MS Aridus (5.00±0.08) × 10-7
II ICP-SFMS Meinhard (7.1±0.9) × 10-7
Aridus (6.5±1.2) × 10-7
USN with desolvator (7.4±1.5) × 10-7
MC-ICP-MS Aridus (5.00±0.09) × 10-7
7.1.2. Minimization of necessary sample volumes for ICP-MS actinide analysis
In the present Ph.D. the capability of DIHEN-ICP-MS and FI-ICP-MS techniques have been
explored in order to minimize the sample volume required for accurate ICP-MS analysis of
actinide in radioactive solution.
7.1.2.1. DIHEN-ICP-MS measurements of uranium standard isotopic reference
materials
In order to characterize the DIHEN in ICP-SFMS for radionuclide analysis the sensitivity for 238U, and 239Pu (in aqueous solution) was studied under hot plasma condition (rf power 1200W;
nebulizer gas flow rate, 0.21 ml min-1) and 90Sr under cold plasma condition in order to avoid 90Zr+ interference (rf power, 750W; nebulizer gas slow rate, 0.35 ml min-1) as a function of
solution up-take rate (see Fig 7.1.4.).
48
Fig 7.1.4. Minimum detectable ratio criteria (3σ) for 236U/238U isotopic ratio of natural uranium for different
nebulizers using H2O and D2O for dilution of the samples
0
200
400
600
800
1000
1200
1400
0 20 40 60 80 100
Solution Up-take rate, μL/min
Sens
itivi
ty,M
Hz/
ppm
U-238Pu-242Sr-90 (cold plasma)
Maximum ion intensity for 238U+ and 239Pu+ was observed at 60 μl min-1. This behavior of 238U+and 239Pu+ for solution uptake rate from 10 to 60 μl min-1 is in agreement with
measurements by McLean et al. [69], using the DIHEN for solution introduction in ICP-SFMS.
In contrast, for 90Sr measurements at cold plasma condition significant lower sensitivity and a
small increasing of sensitivity with increasing solution uptake rate was observed.
In the table 7.1.3. the limits of detection in MilliQ water for selected radionuclides were achieved
with DIHEN nebulizer coupled to ICP-SFMS are summarized.
Table 7.1.3. Calculated Limits of detection (3σ) and absolute sensitivities for selected isotope, achieved for DIHEN-
ICP-SFMS measurements (a Cold plasma condition (in order to avoid 90Zr+ interference))
Isotope LOD, fg ml-1 Absolute sensitivity, counts ml-1
90Sr 35.4a 206.3a
234U 0.46 235U 1.5 236U 0.3 238U 97
1360.3
239Pu 0.43 242Pu 0.9
1281.6
49
Observed LODs were mostly in the sub-fg ml-1 range except for 238U due to a possible
contamination in the solution introduction system and for 90Sr determination because the
measurements were performed under cold plasma condition.
Fig 7.1.5. shows the results of isotope ratio measurements on uranium isotope standard reference
material with natural isotope composition by DIHEN-ICP-SFMS (n=10). The 235U/238 isotope
ratio was found to 0.007227±0.00008 (R.S.D., 1.1%).
Fig 7.1.5 Stability of DIHEN-ICP-SFMS fo r235U238U isotope ratio measurements (Uconc =0.1 ng ml-1, natural
isotopic composition)
0.005
0.0055
0.006
0.0065
0.007
0.0075
0.008
0.0085
0.009
1 3 5 7 9
replicates
U-23
5/U-
238
235U/238U = 0.007227±0.00008 (RSD 1.1%)
235 U
/238 U
isot
opic
rat
io
The precision and accuracy of DIHEN-ICP-SFMS measured on NIST U005, U350, U930 isotope
standard reference materials and U(nat) (Uconc=100 pg ml-1, n=6) are summarized
in table 7.1.4. The accuracy of isotope ratios measured by DIHEN-ICP-SFMS is mostly better
than 1%. The R.S.Ds of the measurements were ranged from 1.1 to 1.4 depending from the ratio
measured.
50
Table 7.1.4. Precision and accuracy of DIHEN-ICP-SFMS measuring uranium isotope standard solutions NIST
U005, U350, U930 and U(nat) (Uconc= 0.1 ng ml-1, n=6).
Measured Certified235U/238U 0.0049435± 3.7e-5 0.0049194 1.42 0.49
U005 234U/238U 0.0000218± 0.8e-6 0.0000219 1.77 -0.12236U/238U 0.0000472± 1.0e-6 0.0000468 4.31 0.94235U/238U 0.540114± 0.002 0.546488 1.63 -1.17
U350 234U/238U 0.003863± 1.1e-4 0.003879 3.25 -0.41236U/238U 0.002644± 0.5e-4 0.002598 1.32 1.78235U/238U 17.347237± 0.007 17.348698 1.98 -0.01
U930 234U/238U 0.2005± 1.7e-3 0.200967 1.89 -0.23236U/238U 0.037831± 1.3e-4 0.037677 2.79 0.41235U/238U 0.007227± 8e-5 0.0072527 1.15 -0.34234U/238U 0.000054± 7e-6 0.00005472 4.10 -0.52
Accuracy (% )
U(nat)
Isotopic ratios Precision (R.S.D., % )
Developed method was applied for determination of 242Pu in pre-concentrated (using MnO2 co-
precipitation) and non-concentrated 10 L of fresh urine as well as 10 L of tap water samples.
Comparative experiments on these samples were also performed using the Meinhard nebulizer
for solution introduction into ICP-SFMS. The results of the measurements are summarized in
Table 7.1.5.
Table 7.1.5. Comparative determination of 242Pu+ in selected sample using DIHEN and Meinhard nebulizer for
solution introduction into ICP-SFMS
Intensity of 242Pu+,cps
15mL of MilliQ
water spiked
with 4pg 242Pu
Pre-concentrated
10L of urine spiked
with 4pg 242Pu
(final volume after
pre-conc. -15 mL)
15mL of MilliQ
water spiked
with 4pg 242Pu
Pre-concentrated 10L
of tap water spiked
with 4pg 242Pu
(final volume after
pre-conc. 15 mL)
DIHEN 46.6 32.3 50.3 49.9
MEINHARD 50.1 35.0 53.1 53.0
Generally, a good agreement (in the range of experimental error) for two nebulizers was observed
in the measured intensities of 242Pu+ in four analyzed samples. However, the sample volumes,
necessary for the successful ICP-SFMS plutonium measurements were 120 μl and 1.2 ml, when
the DIHEN and MEINHARD nebulizers were applied for solution introduction, respectively.
51
7.1.2.2. Application of nano-FI-ICP-MS for determination of actinides at ultratrace
concentration level
A sensitive analytical procedure based on nano-volume flow injection (FI) and inductively
coupled plasma double-focusing sector field mass spectrometry (ICP-SFMS) was developed for
the ultratrace determination of uranium and plutonium.
A 54-nL sample was injected by means of a nanovolume injector into a continuous flow of
carrier liquid at 7 µL min-1 by microconcentric nebulizer DS-5 into ICP-SFMS.
Firstly, the performance of the DS-5 nebulizer has been evaluated. In the Figs. 7.1.6a, b, and c.,
the dependencies of 238U+ ion intensity on the ICP radiofrequency power, nebulizer gas flow rate
and sample uptake flow rate, respectively are shown.
The effect of the ICP radiofrequency power on the sensitivity (Fig. 7.1.6a) is similar to other
nebulizers (with a maximum sensitivity at about 1000 W) because the introduction of aqueous
solution at the flow-rates characteristic of a DS-5 nebulizer does not influence the ICP. In
contrast to other nebulizers, the ion intensity of uranium (238U+) measured as a function of the
nebulizer gas flow rate (Fig. 7.1.6b) is practically constant in the 1.1 – 1.4 L min-1 range after an
increase between 1.00 and 1.05 L min-1. This unique behavior indicates a complete evaporation
of the introduced solution (virtually no aerosol present!) at the nebulizer gas flow rates higher
than 1.05 L min-1. The gas phase introduction results in a remarkable plasma stability because of
the absence of cold-spots induced by larger aerosol droplets. Furthermore complete evaporation
and thus total consumption of the introduced solution by the DS-5 nebulizer is confirmed by the
linearity of the intensity response in the 2.5 – 7 µL min-1 range (Fig. 7.1.6c).
52
Fig. 7.1.6. Effect of a) ICP rf-power (nebulizer gas flow rate: 1.3 L min-1; sample uptake rate: 7 µL min-1); b)
nebulizer gas flow rate (rf-power: 1200 W; sample uptake rate: 7 µL min-1); c) sample uptake rate (rf power: 1200
W; nebulizer gas flow rate: 1.3 L min-1) on the sensitivity for uranium (238U+) in ICP-SFMS using the DS-5 nebulizer
in the continuous flow sample introduction mode.
An important parameter to compare different nebulizers is the absolute sensitivity (number of
counts per femtogram analyte) obtained with the same ICP mass spectrometer. Table 7.1.6
summarizes the sensitivities observed for the different types of nebulizers for the uranium
determination using double-focusing sector field ICP-MS.
The outstanding performance of the DS-5 nebulizer can be explained by the high sample
transport efficiency (total consumption) and high ionization efficiency (absence of aerosol). With
the increasing solution uptake rate the absolute sensitivity of a nebulizer decreases because the
portion of the sample lost to the waste increases and the degrading quality of the aerosol
decreases the ionization. Only the Aridus nebulizer with desolvation shows a similar absolute
sensitivity. The DIHEN nebulizer features the total sample consumption but the quality of aerosol
at an uptake rate of 60 µL min-1 negatively affects the ionization efficiency and thus the absolute
sensitivity.
53
Table 7.1.6: Comparison of the absolute sensitivity of different nebulizer types for 238U+ measured with ICP-SFMS
nebulizer solution uptake rate ml min-1
Sample volume, ml
absolute sensitivity counts fg -1
DS-5 0.007 0.0005* 2418
DIHEN 0.06 0.12 1360
Aridus 0.1 0.2 2600
PFA 0.2 0.4 580
MicroMist 0.2 0.4 820
Meinhard 1 2 97
Figs. 7.1.7 a and b show the transient signals of 238U+ and 242Pu+ for an injection of 54 nL of
aqueous solutions containing 10 pg mL-1 (540 ag absolute) and 1 pg mL-1 (54 ag absolute), of
uranium and 242Pu, respectively, and demonstrate the very high sensitivity of the nano-volume FI-
ICP-SFMS developed. The calibration curves (Fig. 4a and 4b) are linear in the low femtogram
range for 238U and in the sub-femtogram range for 242Pu.
Fig. 7.1.7. Calibration curves of: a) 238U and b) 242Pu determined by nano-volume flow injection ICP-SFMS. The signals shown in the insets correspond to the injection (54 nL) of 10 ng L-1 of uranium and 1 ng l-1 of plutonium
54
238 U
+ ion
inte
nsity
, cps
24
2 Pu+ io
n in
tens
ity, c
ps
10 s
10 s
The relative and absolute limits of detection for 238
U and 242
Pu measured with the developed
nano-volume FI-ICP-SFMS system are summarized in Table 7.1.7. Whereas the concentration
limits of detection in 54 nL sample volume were determined to be 1.6 and 0.3 pg mL-1, the
absolution detection limits were at 91 and 15 ag (10-18 g) for uranium and plutonium,
respectively. The latter correspond to the number of atoms of ~230 000 and ~38 000, for uranium
and 242Pu, respectively, and are, to the author best knowledge, the lowest ever reported.
Table 7.1.7. Relative and absolute detection limits for 238
U and 242
Pu measured with the developed nano-volume FI-
ICP-SFMS system.
relative detection
limits
10-12
g mL-1
absolute detection
limits
10-18
g
absolute detection
limits
10-19
mol
estimated number
of atoms
238U 1.6 91 3.8 ~ 230 000
242Pu 0.3 15 0.6 ~ 38 000
In order to test the developed nFi-ICP-MS procedure the precision and accuracy for isotope ratio
measurements of uranium studied for 10 repeated measurements using 100 pg mL-1 solutions of
NIST U350 and CCLU-500 isotopic standard reference materials. Fig. 7.1.8 shows typical
transient signals of 235U+ and 238U+ as well as calculated 235U+/238U+ isotopic ratio measured for
the CCLU-500 isotope standard material by developed nFi-ICP-MS method. The precision of
transient signal measurements on CCLU-500 laboratory standards (n=10) was better than 2.5%
(RSD).
55
Fig 7.1.8. Flow-injection signals of : a) 235U+ and b) 238U+ recorded for the analysis of the CCLU-500 isotope
standard reference material. c) the calculated 235U/238U isotopic ratio compared with the reference value.
238 U
+ inte
nsity
, cps
23
8 U+ in
tens
ity, c
ps
235 U
/238 U
reference value for 235U/238U = 0.99991
time, s
time, s
injection number
The results obtained for the NIST U350 standard reference material are summarized in Table
7.1.8.
Table 7.1.8. Precision and accuracy of uranium isotope ratio measurements in the NIST U350 standard reference
material (10 injections)
experimental certified R.S.D, % accuracy, %
235U/238U 0.546974 0.54648800 2.3 0.7
234U/238U 0.003703 0.00387900 3.2 -4.5
236U/238U 0.002736 0.00259800 8.0 5.2
The precision of uranium isotope ratio measurement in the NIST U350 increased with the
decreasing of isotope ratio, and, in general was in low % range. The most accurate (of about
56
0.7%) value was measured for the 235U/238U ratio. Taking into account the very small sample
volume analyzed (54 nL), the excellent performance of nano-volume FI–ICP-SFMS method was
observed.
7.2. Determination of long lived radionuclides at ultratrace concentration
level by ICP-MS
During present Ph.D. study a variety of procedures for ICP-MS determination of both
artificial (e.g. Pu, Am, etc) as well as naturally occurred (e.g. U, Th etc) long lived
radionuclides in ultratrace concentration level have been developed. In the following
paragraphs detailed description of the results obtained are presented.
7.2.1. Determination of plutonium, americium and 137Cs at ultratrace level in soil
samples
The depth distribution of plutonium, americium, and 137Cs originating from the 1986 accident at
the Chernobyl Nuclear Power Plant (NPP) was investigated in several soil profiles in the vicinity
from Belarus. The vertical migration of transuranic elements in soils typical of the 30 km
relocation area around Chernobyl NPP was studied using ICP-SFMS as well as alpha and gamma
spectrometry.
Figs. 7.2.1–7.2.4. present experimentally measured distributions of selected radionuclides in soil
profiles of various types sampled in the relocation zone of Masany, Lesok, Dernovichi and
Lomachi (8, 19, 33 and 45 km, respectively, to the north and north-west of Chernobyl NPP). In
general, the concentration of Pu and Am correlated inversely with distance from Chernobyl NPP.
57
Fig 7.2.1. Distributions of plutonium (239Pu+240Pu) and americium (241Am) concentrations in comparison to distribution of 137Cs specific activity (a) and 239+40Pu/137Cs and 241Am/137Cs activity ratios (b) in soil profile collected in Masany. Distance from Chernobyl NPP: 8 km.
Fig 7.2.2. Distributions of radionuclides (a) and activity ratios (b) in soil profile Lesok. 19 km from Chernobyl NPP, plain meadow, light turf-podzol, sand-clay. *Note, that Am concentration is multiplied by 10 in all figures with index (a) for better presentation.
Thus, average plutonium concentration in 10 cm soil layer decreased from 86 pg g-1 at 8 km
(Masany) to 6 pg g-1 at 45 km from Chernobyl NPP (Lomachi). Isotope ratios of 240Pu/239Pu
varied from 0.36 to 0.42 in upper layers of seven soil profiles analyzed.
A sharp decrease of radionuclide concentrations (Am, Pu and 137Cs) with the depth of turf-podzol
soil was observed both in areas close to Chernobyl NPP (Masany, Lesok) and in more distant
locations (e.g. Lomachy). The depth distribution is well-described by an exponential function.
Below a depth of 3–4 cm, a less pronounced decrease of activity is observed.
58
Fig 7.2.3. Distributions of radionuclides (a) and activity ratios (b) in soil profile Dernovichi. 33 km from Chernobyl NPP, bushed meadow in lowered flood land, peat-marsh.
Fig 7.2.4. Distributions of radionuclides (a) and activity ratios (b) in soil profile Lomachi. 45 km from Chernobyl NPP; meliorated massif in a low terrace above water meadow, peat-marsh on a light sedge peat.
Thus, the top soil layer (0–1 cm), including vegetation, contained from 50 to 90% of the
radionuclide inventory, and only minor amounts have penetrated to soil layers below 5 cm. These
results correspond to the results of a the other study [117] where a similar decrease of Chernobyl
NPP derived U concentration with soil depth was also observed for turf-podzol soils, based upon
using 236U as an indicator of Chernobyl uranium.
According to a model of vertical migration of radionuclides [118], there are two main
mechanisms of migration in soil: (1) rapid migration of radionuclides added in a water soluble
form; (2) slow migration of a radioactive substance, which is fixed in hardly soluble soil
complexes or ‘‘hot’’ particles. The results obtained for turf-podzol soils show, that the portion of
actinides migrating slowly is about 80–95%. Hence one can conclude that the main part of
nuclear fuel fallout is contained in low-soluble matrix and the mass transfer of radioactive
substances is very slow. 239+240Pu/137Cs and 241Am/137Cs activity ratios in turf-podzol soil profiles
collected in Masany (at 8 km from Chernobyl NPP) were almost constant within experimental
59
errors down to a 10 cm depth, except for a slight peak of 239+240Pu/137Cs ratio observed at the 5–7
cm depth (Fig. 7.2.1. b), whilst in more distant locations - in Lesok (about 19 km from Chernobyl
NPP) the 239+240Pu/137Cs and 241Am/137Cs activity ratios decreased with soil depth by 3 to 5 folds
(Fig 7.2.2.b). In the close Chernobyl vicinity (Masany) the radioactive fallout consists mainly of
fine-dispersive particles of destroyed nuclear fuel (UO2), aggregates of fuel particles with reactor
graphite and carbon-bitumen particles etc., where both actinides (Pu and Am) and fission
products are ‘‘encapsulated’’. Therefore, the measured activity ratios in Masany soil coincided
with the calculated activity ratios in the core of the Chernobyl reactor[16] which accounts for the
decay of 137Cs and production of 241Am. In this case the radionuclides migrate as a result of
mechanic migration of fuel particles and due to particle destruction, oxidation and leaching
processes. On the contrary, the fallout in Lesok represented a superposition of the fuel component
(UO2 particles) and condensation component (volatile fission products, among them cesium,
captured by atmospheric aerosols), which resulted in generally lower 239+240Pu/137Cs and 241Am/137Cs activity ratios in these soils. In addition, the solubility and mobility of the
condensation component is significantly higher than the mobility of the fuel component,
therefore, the ratio of activities of Am and Pu to the 137Cs activity decreased further with the soil
depth in Fig. 7.2.2b.
A very similar distribution of Pu, Am and Cs radionuclides down to 7 cm was observed in soil
profiles collected in Dernovichi (Fig.7.2.3). However, activity ratios 239+240Pu/137Cs and 241Am/137Cs increased significantly in the profile below 7 cm. Obviously, this increase cannot be
explained by plutonium from global fallout, because measured Pu concentration in deeper soil
collected in Dernovichi exceeds the global fallout concentration by more than one order of
magnitude compare, for instance, with 7–10 cm layer collected in Lomachi, (Fig. 7.2.4a).
Contaminations of deep soil layer in Dernovichi with Pu and Am are similar and might be due to
mechanical transfer of contaminated upper soil shortly after the Chernobyl accident. It should be
mentioned, that the relocation zone included initially only areas within 30 km around Chernobyl
NPP.
7.2.2. Determination of Pu at at ml-1 level in urine
Because the plutonium concentration in the urine sample is expected to be relatively low (< 10-15
g ml-1 [12]) a new analytical procedure has been developed permitting determination of Pu in
60
urine at the low attogram per mL (10-18 g ml-1) concentration level using ICP-SFMS. One liter of
urine doped with 4 pg 242Pu was analyzed after co-precipitation with Ca3(PO4)2 followed by
extraction chromatography on TEVA resin in order to enrich the Pu as well as to remove uranium
and other minor matrix elements, that disturb the correct ICP-SFMS determination of plutonium
(see Fig 7.2.5).
Fig.7.2.5. Influence of U concentration on the background signal on m/z 239 u
0.010
0.100
1.000
10.000
100.000
0 5 10 15 20 25 30 35 40 45 50
Concentration of U, ppt
Lg in
tens
ity o
n m
/z 2
39, c
ps
Concentration of U, μg l-1
Bac
kgro
und
inte
nsity
on
m/z
239
u
The efficiency of the co-precipitation and separation procedure in terms of the removal of matrix
ions, as well as U, is shown in Table 7.2.1 The concentrations of minor elements in the sample
after pre-concentration and separation were significantly lower (two orders of magnitude) than in
the original urine. U concentration was determined to be 0.2 pg mL-1, and, no increase of the
background on m/z 239 u was observed.
The recovery obtained was about 70%, while enrichment factors of 100 and 1000 were achieved
for measurements with the PFA-100 and DIHEN nebulizer, respectively.
61
Table 7.2.1. Concentration of minor matrix elements and uranium in urine before calcium phosphate co-precipitation
and after separation on TEVA resin
Concentration, μg ml-1Element
Before co-
precipitation After separation
Decontamination
factor
Na 38.2±1.9 0.72±0.1 ~53
Mg 31±1.4 0.75±0.5 ~41
K 163±28 2.6±0.1 ~63
Ca 770±70 1.24±0.05 ~620
Fe 0.222±0.002 0.09±0.01 ~2.5
U (4.1±0.1)±10-5 (0.2±0.05)±10-6 ~200
Precision and accuracy of the developed method was studied on “blank urine” (fresh urine,
subjected to the same co-precipitation and separation steps as the samples) solution spiked with
100±11 fg mL-1 of 239Pu. The precision assessment was based on 10 repeated measurements of
this synthetically prepared standard achieving an accuracy of 2.5%. Short-term stability (n=10) of
these measurements is presented in Fig.7.2.6. precision was determined to be 7 % (RSD).
To further evaluate the accuracy of developed ultrasensitive method the ICP-SFMS
measurements of 240Pu/239Pu isotopic ratio in urine, spiked with synthetically prepared standard
solution, were studied with PFA-100 and DIHEN nebulizers.
62
020406080
100120140160180200
0 1 2 3 4 5 6 7 8 9 10
replicates
239 Pu
con
cent
ratio
n, fg
ml-1
239 Pu
con
cent
ratio
n, fg
ml-1
Fig. 7.2.6. Short-term stability of 239Pu in synthetically prepared standard solution.
The results of these measurements show a good agreement (see Table 7.2.2) between the
expected and measured values of the 240Pu/239Pu isotopic ratio in measured urine solution. A
precision (RSD, %, n=10) of 1.8% and 1.9% and an accuracy of 1.5% and 1.8% were determined
for the PFA-100 and DIHEN nebulizers, respectively.
Table 7.2.2. 240Pu/239Pu isotopic ratio measurements in synthetically prepared urine laboratory standard solution
using PFA-100 and DIHEN nebulizers for solution introduction into double focusing ICP-SFMS
240Pu/239Pu isotopic ratio Nebulizer
measured expected
Precision, % Accuracy, %
PFA-100 0.1445±0.004 1.85 1.55
DIHEN 0.1448±0.004 0.1423±0.0003
1.78 1.78
The figures of merits, such as sensitivity, abundance sensitivity and limit of detection in the
developed method for Pu determination were studied using the PFA-100 and DIHEN nebulizers
for sample introduction into ICP-SFMS. A slightly higher sensitivity (1.4 fold) was observed
with the PFA-100 nebulizer in comparison to the DIHEN nebulizer, whereas the absolute
63
sensitivity was 6.6-fold better with the DIHEN nebulizer (see Table 7.2.3) and thus
demonstrating the significance of applying this nebulizer for small or hazardous samples.
Table 7.2.3. Figures of merit of double focusing ICP-SFMS for Pu determination using PFA-100 and DIHEN
nebulizers for sample introduction
LOD (3σ) ,
10-18g mL-1
Solution
uptake
rate,
mL min-1
Sensitivity
for Pu,
MHz
ppm-1
Absolute
sensitivity
for Pu,
counts fg 1
Uranium
hydride
formation
rate, UH+/U+
Abundance
sensitivity
mm 1+ 239Pu 242Pu
PFA-100 0.58 2000 207 1.3×10-4 2.01×10-5 9 8
DIHEN* 0.06 1380 1380 1.2×10-4 2.02×10-5 1.02 0.9
*Calculated LODs for 239Pu and 242Pu assumed pre-concentration of the sample after evaporation from 5 mL (used
for PFA-100 nebulizer) to 0.5 mL (used for DIHEN)
The uranium hydride formation rate and abundance sensitivity remained the same for two
selected nebulizers, hence ensuring a negligible increase of the background on m/z 239 u.
The LOD (3σ-criterion ) for Pu determination was calculated using the intensity values on the
m/z 239 u and m/z 242 u measured in “blank urine” solution as well as the sensitivity for Pu in
ICP-SFMS with the selected nebulizer. Because the solution uptake rate of the DIHEN nebulizer
(0.06 mL min-1) is about 10 times lower than in the PFA-100 nebulizer (0.58 mL min-1), 5 mL of
the analyzed sample was evaporated to the volume of 0.5 mL for the DIHEN measurements. By
applying this approach, the analysis time of the measurements with the PFA-100 and DIHEN
nebulizers as well as the consumption of the original sample remained the same. Obtained LODs
for 239Pu and 242Pu in urine for two selected nebulizers are summarized in Table 7.2.3. In the case
of the DIHEN nebulizer, the calculation assumed a 10-fold concentration of the sample due to
evaporation. Limits of detection for 239Pu in urine with the PFA-100 and DIHEN nebulizers were
9×10-18 g mL-1 and 8×10-18 g mL-1, respectively, whereby for 242Pu values of 1.02×10-18 g mL-1
and 0.9×10-18 g mL-1 were achieved.
64
7.2.3. 226Ra determination in mineral water samples
In the present work, an analytical procedure for determination of 226Ra at the low femtogram per
ml concentration level in mineral water samples using double focusing sector field ICP-MS have
been proposed. In the following paragraph the detailed description of the developed method is
presented.
Using direct ICP-SFMS determination the limit of detection LOD (3σ-criterion, n=6) for 226Ra in
high-purity MilliQ water was found to be 0.22 fg ml-1. In order to study the influence of possible
isobaric interferences at m/z 226u (see Table 7.2.4) on the LOD determined for 226Ra a synthetic
laboratory standard solution containing 100 ppb of Sr, Ba, Mo La, Ce, Pb, and W was analyzed.
Table 7.2.4. Possible interferences for determination of 226Ra by ICP-MS, required mass resolutions as well as
influence of selected trace elements on the LOD for 226Ra in the analytical method developed.
Interference Required mass
resolution (m/Δm)
*LOD for 226Ra, fg
ml-1
88Sr138Ba+ 1054 0.95 87Sr139La+ 1076 0.6 86Sr140Ce+ 1072 0.75 206Pb18O+ 4557 2.4 186W40Ar+ 2080 5.4
209Bi16O1H + 5347 23 97Mo129Xe+ 1053 94Mo132Xe+ 1046 92Mo134Xe+ 1060 95Mo131Xe+ 1054 98Mo128Xe+ 1044 96Mo130Xe+ 1041 100Mo126Xe+ 1058
**0.35
*Concentration of selected trace elements was 100 ng ml-1
**The presented value corresponds to the total contribution of all molybdenum isotopes on LOD for 226Ra.
The highest molecular ion formation rate were found for 186W40Ar+ and 209Bi16O1H+ species that
resulted in an increase of the LOD for 226Ra determination of 5.4 fg ml-1 and 23 fg ml-1,
65
respectively (for concentrations of W and Bi of 100 ng ml-1). However, such high concentrations
of W and Bi in natural mineral water are not likely, in contrast to the Sr, Ba and Pb concentration.
Due to the contribution of “Sr-based” (e.g. 88Sr138Ba+, 87Sr139La+, 86Sr140Ce+ ) and 206Pb18O+
molecular ions to the background signal on m/z 226 (for 100 ng ml-1 of Sr, Ba, La, Ce and Pb), an
increase in the LOD for 226Ra to 2.3 fg ml-1 and 2.4 fg ml-1, respectively, can be expected.
Although the “Sr-based” interferences can be successfully separated from the 226Ra+ ions by
measuring in Medium Resolution mode (see Tabele 7.2.4.), the lose of sensitivity in compare to
Low Resolution mode could not be afforded for the low concentration level of 226Ra in analyzed
samples. Therefore, in the present experiments, before the measurements of the mineral water
samples the radium was pre-concentrated and separated from the matrix elements using a tandem
of a laboratory-prepared filter, based on MnO2, and Eichrom “Sr-specific” resin (see Fig. 6.10).
The recovery of 226Ra was evaluated in the following way. Two times of nine aliquots of 0.2l of
mineral water sample were spiked by 5 fg and 50 fg of 226Ra, respectively. The average
recoveries obtained for these spiked solutions were determined to be 69±8% and 72±6%,
respectively. Using these data, the mean recovery of 71.5% was further used to correct the
measured radium concentration.
The pre-concentration and separation procedures of Ra were studied on the synthetically prepared
standard solution of 10 ng ml-1 of Sr, Ba, Pb, Bi and W as well as 10 fg ml-1 of 226Ra (see Table
7.2.5.). In order to pre-concentrate radium from the analyzed solution a laboratory-prepared filter,
based on MnO2, was used.
Because of the relatively good and reproducible recoveries as well as the low preparation cost,
the filter utilized was found to be very useful for the pre-concentration of radium in comparison
to the expensive commercially available Empore “Ra-specific disk”. Moreover, using this disk,
effective separation of 226Ra from the Mo, W, Bi and, in part, from Pb was observed. However,
because of the similarity of alkaline elements Sr and Ba were also retained on the filter. To
further purify the radium (mainly from Sr) the sample was send through the Eichrom Sr Spec®
and collected for ICP-SFMS measurements (assuming that Sr is retained in the resin).
The total separation factor (overall separation on the “Ra specific disk” and Eichrom Sr Spec®)
of the method developed for Sr, Mo, Ba, Pb, Bi, and W was found to be 330, 850, 3.2, 60, 770
and 720, respectively, while the recovery of radium was determined as 71.5%. The limit of
detection (3σ) and limit of quantification (10σ) for 226Ra were determined as 0.02 and 0.06 fg ml-
1, respectively, using a 100 fg ml-1 standard of 226Ra and a tenfold pre-concentration factor. The
66
accuracy and precision of 226Ra+ measurements (RSD, n=10) for 25 fg ml-1 of 226Ra standard
were 1.7% and 2.1%, respectively.
Table 7.2.5.. Concentration of trace elements including radium in synthetically prepared standard solution of 10 ng
ml-1 of Sr, Mo, Ba, Pb, Bi and W as well as 10 fg ml-1 of 226Ra after pre-concentration and separation steps
Concentration, ng ml-1
Element In standard
solution
*After pre-
concentration onto
“MnO2 filter”
After separation on
“Sr-specific” resin
Separation
factor
Sr 10 2.4±0.1 0.03±0.002 ~330
Mo 10 0.032±0.003 0.012±0.001 ~850
Ba 10 24±1.4 3.10±0.09 ~3.2
Pb 10 1.40±0.09 0.17±0.01 ~60
Bi 10 0.016±0.003 0.013±0.003 ~770
W 10 0.015±0.002 0.014±0.002 ~720
Ra 10×10-6 (75.2±3)×10-6 (70.4±3)±10-6 -
*Taken into account ten-fold pre-concentration
Developed analytical procedure was applied for determination of radium the different water
samples. Nine different types of bottled mineral water samples (of different brands commercially
available in Germany) and four samples from ground water sources (Erzgebirge, Germany) were
analyzed by ICP-SFMS for their 226Ra concentration by the method developed. The results of
these measurements are summarized in Table 7.2.6, which shows that the radium concentrations
in all investigated waters were lower than 5 fg ml-1, except for two mineral water samples where
the concentrations of 226Ra were 10.3 and 14.2 fg ml-1, respectively. According to the EPA
regulation standards[119], these values are about two to three times higher than the suggested
maximum concentration level of radium.
67
Table 7.2.6. Concentration of 226Ra and U in samples of mineral water (MW) and ground water (GW)
analyzed by ICP-SFMS.
Sample
226Ra
concentration,
fg ml-1
U concentration,
ng ml-1
MW-1 <0.02 0.022±0.006
MW-2 0.8±0.4 0.111±0.007
MW-3 1.4±0.4 0.73±0.05
MW-4 <0.02 0.020±0.009
MW-5 0.7±0.4 0.37±0.04
MW-6 1.6±0.9 0.79±0.03
MW-7 <0.02 0.010±0.007
MW-8 10.3±1.0 17.3±0.9
MW-9 14.2±0.9 19.2±0.6
GW-1 2.1±0.4 0.71±0.04
GW-2 0.9±0.3 0.29±0.03
GW-3 1.7±0.5 0.52±0.04
GW-4 4.8±0.8 5.2±0.8
Tap water <0.02 0.481±0.012
*uncertainties given include the uncertainties of co-precipitated, separated and measurement procedure
Because 226Ra occurs in natural samples from the radioactive decay series of 238U that could also
present a source of potential health impact (mainly 234U and 235U) [120], in addition, the
concentrations of uranium in all analyzed samples were measured (see Table 7.2.6).
The uranium concentrations determined were correlated with the concentrations of radium and, in
general, were relatively low (in the range of 0.001 to 0.79 ng ml-1). However, in the samples
where elevated concentrations of radium were found the concentrations of U were 17.3 ng ml-1
and 19.2 ng ml-1 (about 50 times higher than in tap water). Measured 235U/238U isotope ratios in
the range of 0.00715 to 0.00727 (with RSD from 0.08 to 1.4%, n=6) show that in all investigated
samples the uranium was of natural origin. Using the correlation between the 226Ra and U
68
content, it might be, perhaps, quick and relatively easy by screening of mineral waters for U to
preliminary establish the significant “226Ra risk” in real world application. However, in this case,
due to the possible isotope variation of Ra in nature, a careful study of this approach is required.
The effective dose contribution was calculated using the radionuclide concentrations and the dose
conversion factors from WHO[121] for consumption of 1 l d-1 mineral water. The results of these
calculations, presented in Fig. 7.2.7., show that in all measured samples the committed effective
dose due to the consumption of mineral water does not exceed the limit recommended by WHO
(0.1 mSv y-1 from the gross alpha).
Fig 7.2.7. Calculated effective radioactive dose for adults based on the concentration of 226Ra, 234U and 238U and the
dose conversion factor from the WHO (1993)[121].
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
MW-1 MW-2 MW-3 MW-4 MW-5 MW-6 MW-7 MW-8 MW-9 GW-1 GW-2 GW-3 GW-4 Tapwatersample
Effe
ctiv
e do
se, m
Sv
year
-1 Ra-226 U-234 U-238
*The dose is calculated with respect to water consumption of 1l d-1.
However, it should be noted here that the effective dose in the present study is calculated
assuming 1 l d-1 water consumption and the above-mentioned WHO limit is based on 2 l water
intake per day.
69
7.2.4. Routine determination of naturally occurred long lived radionuclide in urine
samples
During the Ph.D. study a number of experiments have been devoted in order to develop an
analytical method for the routine determination of naturally occurred long-lived radionuclide
such as 232Th, 234U, 235U and 238U in human urine, that is required for the radiation protection and
nuclear safeguards. The advantage of the analytical techniques to be developed should be to save
time, especially by reducing the efforts required for sample preparations as well as reducing the
contamination involved in sample preparation. To provide this, relatively easy sample preparation
procedure (using microwave digestion) have been applied in order to decompose the fresh urine
samples prior to ICP-SFMS determination (see paragraph. 6.3.3).
To further minimize the operation time required the sample were introduced into ICP-MS using
the auto sampler ASX-500 (Cetac Technologies, USA) and, usually, were measured overnight.
The LODs (3σ-criterion) for some radionuclide of interest in urine samples calculated for
developed procedure is summarized Table 7.2.7.
Table 7.2.7. Ion intensity in the procedural blank (2% HNO3) and calculated limits of detection for selected
radionuclides measured by developed ICP-SFMS method.
Radionuclide Ion intensity in 2%
HNO3LOD, fg ml-1
232Th´ 124 49.8 234U 0.2 0.07 235U 0.3 0.9 238U 158 52.2
In general, determined LODs for 238U and 232The are higher than those ones for 234U and 235U,
which can be explained by lower background signal in the blank solution.
In order to evaluate accuracy and precision of the developed method the synthetic matrix-
matched laboratory standard solution was prepared for external calibration and was used for
multitude of routine measurements.
70
The one of the results sets for analysis of urine samples by ICP-SFMS is summarized in Table
7.2.8. In total, 10 fresh urine samples as well as quality control synthetic prepared laboratory
standard were measured by the developed method for its Th and U content.
Table 7.2.8. Results of determination of uranium and thorium concentration developed ICP-SFMS procedure (n=6).
Uranium measurements Thorium measurements Sample
U, ng ml-1 R.S.D., % Th, ng ml-1 R.S.D.,
1 0.130 2.3 0.051 4.1
2 0.231 2.4 0.210 2.1
3 0.072 3.6 0.076 3.2
4 0.062 3.7 0.102 2.7
5 0.195 2.7 0.210 2.9
6 0.106 2.9 0.032 3.9
7 0.128 2.6 0.089 3.7
8 0.189 2.3 0.124 2.4
9 0.120 2.6 0.109 2.8
10 0.152 2.8 0.085 3.4
Synth. prepared
urine standard
solution*
0.170 2.1 0.162 2.3
* expected values of uranium and thorium concentration in synthetic prepared urine standard solution were
0.110±0.009 and 0.152±0.008, respectively.
The uranium and thorium concentration in examined urine samples varied between 0.062 to
0.231 ng ml-1 and from 0.051 to 0.210 ng ml-1, respectively. The measurements of synthetic
prepared urine standard solution result the accuracy for U and Th of 3.5% and 6.1%, respectively,
which was acceptable for the sample with such high salt content in the matrix. The total
analyzing time required for the measurements of the 10 urine samples (including the sample
preparation) was about 45 min.
71
7.3. Isotope ratio measurements of long lived radionuclides by ICP-MS
In addition to the measurements of concentration of long-lived radionuclides, the analytical
methods for determination of their isotopic ratios were developed during present Ph.D. study. In
the following paragraphs the detailed description and possible application of the methods
developed are presented.
7.3.1. Determination of the source of contamination of Ashtabula River via the
measured 236U/238U and 235U/238U isotopic ratio
Uranium contamination of anthropogenic origin has been identified in unconsolidated sediments
of the Ashtabula River, USA. The concentrations of U were about 188 µg/g in dry sediment. In
order to access the source of contamination the uranium isotopic ratios of 236U/238U and 235U/238U
in the sampled sediments collected in Ashtabula River were measured by ICP-SFMS. The results
of these measurements on collected 11 samples are presented on Fig 7.3.1. Lowered 235U/238U
isotopic ratios indicate that the uranium is largely but not exclusively of natural composition.
Samples with slightly depleted 235U also contain elevated 236U concentrations (see Fig. 7.3.1). It
is assumed that contamination occurred during the post-1964 time frame due to at least two
Fig 7.3.1. Dependences isotope ratios of 236U/238U in 235U/238U isotope ratio.
236U/238U
000100200300400500600700800901
0.0058 0.0063 0.0068 0.0073
0.000.000.000.000.000.000.000.000.000.00
0.0078
Isotope ratio 235U / 238U
Isot
ope
ratio
236 U
/ 238
U
72
distinct sources of anthropogenic U contamination: a) discharges from the processing of enriched
and depleted U metal by a DOE (Department of Energy) contractor facility and b) U-bearing
wastes from the production of TiO2 from limonite and associated minerals.
These isotopic methodologies are potentially useful in settings where releases of non-natural 235U/238U composition materials and/or "naturally occurring radioactive material" (NORM) have
taken place.
7.3.2. Pu isotope ratio measurement in environmental sample
An analytical method for the determination of plutonium isotope ratios at ultratrace level in Sea
of Galilee by inductively coupled plasma mass spectrometry (ICP-MS) is proposed. Because of
the very low concentration of Pu and high salt content of the measured sample the successful
preconcentration and separation procedure was applied before the ICP-MS determination (see Fig
6.7). 242Pu spike was used to indicate the efficiency of the co-precipitation and separation of the
plutonium in the developed method. A concentration of dissolved plutonium in 100 L of water
sample from the Sea of Galilee was estimated to be approximately 21 ag mL-1 (5*10-9Bq ml-1).
Using a co-precipitation procedure based on MnO2 and Fe(OH)3 concentration factors of more
than 6600 were achieved. Procedural recovery of 242Pu spike from 100L of Sea of Galilee was
found to be about 62%.
Precision and accuracy of the 240Pu/239Pu isotope ratio of the developed method was studied using
a synthetically prepared Pu standard solution (see Table 7.3.1).
Table 7.3.1. 240Pu/239Pu isotopic ratio in synthetically prepared laboratory standard solution measured by ICP-SFMS
240Pu/239Pu isotopic ratio Nebulizer
measured expected
Precision, % Accuracy, %
PFA-100 0.3002±0.0038 0.2960±0.0026 0.9 1.3
The results show sufficient agreement between the expected and measured values of the 240Pu/239Pu isotopic ratio with a precision (RSD, n=10) and accuracy of 0.9% and 1.3%,
73
respectively, which are comparable to our previous results. Precision of 5% was determined from
ten independent measurements of 100 fg mL-1 of 242Pu solution.
The optimized analytical method was applied for the measurement of the 240Pu/239Pu isotopic
ratio in water from the Sea of Galilee. Comparative measurements performed by ICP-SFMS and
MC-ICP-MS (Nu-Instruments, installed in the analytical laboratory of Geological Survey of
Israel, Jerusalem, Israel) are summarized in Table 7.3.2.
Table 7.3.2. Concentration of 239Pu and 240Pu/239Pu isotopic ratio measurements in the water sample from the Sea of
Galilee, measured by ICP-SFMS (Element) and MC-ICP-MS (Nu-Plasma). ICP-MS Nebulizer 239Pu concentration, g mL-1 240Pu/239Pu
ICP-SFMS PFA-100 3.3±1.0 10-19 0.33±0.14
MC-ICP-MS Aridus 3.9±0.1 10-19 0.17±0.05
The 240Pu/239Pu isotopic ratio measured by MC-ICP-MS was determined as 0.17±0.05, which
represents the value of contamination of the Sea of Galilee due to the global fallout after nuclear
weapon tests in the sixties. Using ICP-SFMS, the 240Pu/239Pu isotopic ratio was found to be
0.33±0.14 (short term repeatability). This deviation could be explained by a very low
concentration of 240Pu in the sample and a higher detection limit of ICP-SFMS with a single ion
collector in comparison to MC-ICP-MS. Therefore, MC-ICP-MS has the advantage of analyzing
the 240Pu/239Pu isotopic ratio with good accuracy and precision at the low ag mL-1 concentration
level. In future, processing of the larger samples could be of interest in order to obtain more
precise 240Pu/239Pu isotopic ratio.
7.3.3. Routine determination of 234U/238U and 235U238U isotopic ratios by ICP-
SFMS
Besides the determination of U content the method for precise and accurate of uranium isotopic
ratio measurements have been developed and successfully established for ICP-SFMS analysis of
urine sample.
74
For quality assurance of the method the uranium isotopic standard reference material NIST U005,
U350, U930 were measured (see Table 7.3.3). The accuracies for determined uranium isotopic
ratios were ranged from 0.003 to 0.895, depending on abundance of measured isotopes. For
instance, for NIST U930 standard reference material the accuracy for 236U/238U isotopic ratio was
determined to be 0.87%, while for 235U/238U isotopic ratio the value of 0.028% was yielded.
Table 7.3.3. Results of ICP-SFMS measurements of uranium isotopic ratio in selected isotopic standard reference
material
SRM Measured Certified Accuracy, %1 U005 235U/238U 0.00491± 3.7e-5 0.0049194 0.003
234U/238U 0.0000218± 0.8e-6 0.0000219 -0.145236U/238U 0.000047± 1.0e-6 0.0000468 0.895
2 U350 235U/238U 0.544± 0.002 0.546488 -0.351234U/238U 0.0038± 1.1e-4 0.003879 -0.43236U/238U 0.00261± 0.5e-4 0.002598 0.837
3 U930 235U/238U 17.353± 0.007 17.348698 0.028234U/238U 0.201078± 1.7e-6 0.200967 0.055236U/238U 0.037347± 1.5e-6 0.037677 0.873
The developed method was used for precise and accurate uranium isotopic ratio analysis of
multitude urine samples. Table 7.3.4 presents the illustration of typical ICP-SFMS determination
of 234U/238U and 235U238U isotopic ratios in received urine samples (10 samples).
Generally, determined uranium isotopic ratio in analyzed urine samples were of natural
composition (235U/238U = ~ 0.00725) except of two samples, where the slightly depleted uranium
was detected.
The developed analytical method is of interesting for nuclear monitoring and nuclear safeguards
as well as promise to be very attracting for forensic applications where only a small amount of
urine sample is available for the investigation.
75
Table 7.3.4. Results of determination of 234U/238U and 235U238U isotopic ratios in analyzed urine samples using
developed ICP-SFMS procedure (number of repeated measurements per sample -n=6).
Sample 234U/238U
(±R.S.D)
235U/238U
(±R.S.D)
1 5.0 (±0.2) ×10-5 0.0070 (±0.005)
2 6.3 (±0.5) ×10-5 0.0065 (±0.004)
3 7.1 (±0.7) ×10-5 0.0067 (±0.004)
4 5.6 (±0.4) ×10-5 0.0074 (±0.002)
5 5.1 (±0.1) ×10-5 0.0076 (±0.003)
6 4.5 (±0.5) ×10-5 0.0075 (±0.002)
7 5.3 (±0.3) ×10-5 0.0072 (±0.004)
8 5.2 (±0.4) ×10-5 0.0071 (±0.001)
9 5.7 (±0.5) ×10-5 0.0074 (±0.002)
10 5.4 (±0.3) ×10-5 0.0073 (±0.004)
Synth. prepared
urine standard
solution*
5.6 (±0.2) ×10-5 0.0073 (±0.003)
Natural value 5.472×10-5 0.0072527
* expected values of 234U/238U and 235U238U isotopic composition in synthetic prepared urine standard solution were
5.4 ×10-5 and 0.00725, respectively.
7.4. ICP-MS determination of 90Sr
7.4.1. Improvement of LOD for 90Sr by decreasing of background signal on m/z 90
The detection limit, accuracy and precision of 90Sr determination in ICP-MS are mainly affected
by the occurrence of isobaric atomic and molecular ions that increase the background signal at
m/z 90 (see Table 7.4.1).
76
Table 7.4.1. Possible interferences for 90Sr radionuclide and required mass resolution for its resolving on ICP-SFMS
Nuclide Molecular ions Required mass
resolution (m/Δm) 90Sr 180W++ 1370
180Hf++ 1372
58Ni16O2+ 2315
74Ge16O+ 10765
52Cr38Ar+ 19987
50V40Ar+ 49894
54Fe38Ar+ 155548
50Ti40Ar+ 158287
90Zr+ 29877
Moreover, the peak tailing of the highly abundant 88Sr isotope – strontium of natural isotope
composition is usually present in the sample in the low ppm range – will also disturb the
ultrasensitive 90Sr determination. In the following experiment an effort to improve the
background signal for ICP-SFMS 90Sr measurements have been performed The developed
technique was applied for analysis of ground water samples, collected in Kazakhstan for it’s 90Sr
content.
7.4.1.1. Application of medium mass resolution mode (R=4000)
In order to minimize isobaric interferences and peak tailing on m/z 90 the ICP-SFMS
measurements 90Sr were performed in the medium mass resolution mode (m/Δm =4400). Under
these experimental conditions, the abundance sensitivity of two mass units ((m+2)/m) in medium
resolution mode was found to be 7×10-7 (versus 2×10-5 in low mass resolution mode) by
measuring 1 mg ml-1 of natural strontium in the way described in paragraph 7.1.1. However,
whereas several isobaric interferences (e.g. 180Hf++, 58Ni16O2+) can be resolved from 90Sr at a
mass resolution of 4400, the required mass resolution for most of the interferences at m/z 90 are
higher than that of ICP-SFMS (see Table 7.4.1), so some additional approach should be applied.
77
7.4.1.2. Cold plasma technique
Another alternative way of removal of isobaric interferences is the use of cold plasma (plasma
which works at lower forward powers in an effort to suppress ionization of elements of higher
ionization potential). It should be noted here, among others (see Table 7.4.1), the elimination of
isobaric interference of 90Zr+ and “Ar-based interferences” (e.g. 52Cr38Ar+, 50Ti40Ar+, etc) are of
special interest due to their relatively high abundance. The ionization potentials of strontium and
zirconium are 5.7 eV and 6.8 eV, respectively, therefore Zr1 could theoretically be suppressed
under cool plasma conditions. Moreover removing of “Ar-based interferences” may be also
successfully achieved by operation at low forward power, as was stated by Vanhaeecke et al
[122].
In the present experiment the effect of rf power on the intensity of 88Sr+ ions and the background
signal on m/z 90 (see Fig 7.4.1.) was studied using 10 ppb of Sr, Zr and 100 ppb Ge, Cr, V, Fe, Ti
solutions. Optimized forward power was found to be 650 W, where the sensitivity for Sr+ of 18
MHz ppm-1 and the background signal on m/z 90 below 0.8 cps were achieved.
Fig. 7.4.1. Effect of rf power on the response of 88Sr+ and background intensity signal on m/z=90
(Note that ion intensity signal on m/z=90 is presented on a logarithmic scale)
0
50000
100000
150000
200000
250000
300000
600 700 800 900 1000
rf power, W
88Sr
+ ion
inte
nsity
, cps
0.1
1
10
100
1000
10000
100000
1000000
log
ion
inte
nsity
on
m/z
=90,
cps
Sr-88 ion intensityZr-90 ion intensity
88Sr+ ion intensity background signal on m/z 90
78
In addition to the optimization of rf-power, further ICP-SFMS tuning was carried out with respect
to the nebulizer gas flow rate, ion focus lens voltage and XYZ torch position (see Fig 7.4.2).
Firstly, nebulizer gas flow was slightly increased (up to 1.2 l min-1) to ensure additional cooling
of the plasma and, therefore, a further reduction of “Ar-based interferences” [122]. A small
incfrease in Sr+ ion intensity was found. After that, the focus lens voltage was optimized, as it
corrects for differences in the ion kinetic energy and, therefore, differs between hot and cold
plasma. A two fold increase in sensitivity for Sr was observed by changing the focus lens
potential from -850 V (which was optimal for hot plasma) to a more negative -1100 V.
Finally, after tuning the XYZ position, a sensitivity for Sr in ICP-SFMS of 42 MHz ppm-1 under
cold plasma conditions was achieved, while the background on m/z remained below 0.8 cps. The
limit of detection (3σ-criterion) and limit of quantification (10σ-criterion) for 90Sr under these
optimized parameters was determined to be 11 fg ml-1 and 35 fg ml-1, respectively.
Fig. 7.4.2. Effect of optimized nebulizer gas flow rate, focus lens voltage and XYZ-position on the 88Sr+ ion intensity
under cold plasma conditions
owever, if the application of medium mass resolution of ICP-SFMS and cold plasma conditions
0
50000
100000
150000
200000
250000
300000
350000
400000
450000
500000
0 5 10 15 20number of measuremets
88S
r+ Ion
inte
nsity
, cps
Sr-8888Sr+
Optimized rf power (650W)
optimized nebulizer gas flow rate (1.2 l min-1)
optimized focus lens voltage (-1100V)
optimized XYZ position
number of measurements
88Sr
+ ion
inte
nsity
, cps
H
sufficiently reduce the influence of isobaric interferences on m/z=90, the peak tailing of 88Sr+
seems to be the critical factor in the determination of 90Sr using the developed method. If the
concentration of natural strontium in the sample is higher than 25 ng ml-1, which is very often
79
case, then other strategy would be necessary (e.g. use of MC-ICP-MS with better abundance
sensitivity).
7.4.2. Determination of 90Sr in environmental samples
he optimized method was tested for determination of 90Sr in four ground water samples
r were determined in analyzed ground
able 7.4.2. Concentration of selected elements in analyzed ground water samples measured by ICP-
ns
Concentration, ng ml-1
T
collected from different contaminated areas of the Semipalatinsk Test Site (STS) (Kazakhstan).
The measurements were performed in the following way.
Firstly, the concentrations of Ti, V, Cr, Fe, Ge, Sr and Z
water samples analyzed using common hot plasma conditions (see Table. 7.4.2).
T
SFMS (m/Δm=4400, rf power =1200 W) in medium mass resolution mode under hot plasma conditio
Element Sample 1 Sa 3 Sample 4
LOD,
mple 2 Sample ppb
Ti <LOD <LOD <LOD <LOD 0.2
V 0.2 0.7 0.3 <LOD 0.01
Cr 0.1 0.1 0.5 0.2 0.07
Fe 6.1 9.7 17 7.1 0.5
Ge <LOD <LOD < < LOD LOD 0.08
Sr 5.8 6.0 2.2 5.9 0.09
Zr 0.1 0.2 2.5 < LOD 0.01
U 7414 5796 1 8638 4935 .9×10-5
he concentration of natural strontium in the samples ranged from 2.2 ng ml-1 to 6.0 ng ml-1,
T
while concentrations of other measured elements were below 17 ng ml-1. Based on these results,
for each of the analyzed samples, matrix-matched aqueous standard solutions with a similar
composition and concentration of Sr, Ti, V, Cr, Fe, Ge, and Zr were prepared, and were further
used as procedural blanks for 90Sr measurements . Moreover, because the concentration of 88Sr in
80
the samples was lower than 25 ng ml-1, the ground water samples and also synthetic standards
were subjected to a pre-concentration procedure using SEP 60 IR (assuming a pre-concentration
factor of five). Recovery using the experimental procedure was determined as 82% using 88Sr.
After pre-concentration, the 90Sr in the samples was determined by ICP-SFMS with cold plasma
ig. 7.4.3. Ion intensities on m/z=88 and m/z=90 measured in pre-concentrated procedural blank, sample 1 solution
, 0.1, 6.1, 5.8, 0.1 ng ml-1 of V, Cr, Fe, Sr, Zr,
ecause the concentration of the elements that may cause the formation of isobaric interferences
on m/z=90, as well as the concentration of natural Sr, was equivalent in all measured solutions,
conditions. Mass-to-charge ratios of 88 and 90 were monitored. The analyzed ground water
sample and three pre-concentrated procedural blanks, spiked with 50, 100 and 200 fg ml-1 of 90Sr
standard, respectively, were measured one after the other in one ICP-MS run and with washing
by appropriate pre-concentrated procedural blank steps in between. Typical results of these
measurements (e.g. for sample 1) are presented in Fig 7.4.3.
Fand procedural blank spiked with 50, 100 and 200 fg ml-1 of 90Sr
*Bpr – procedural blank for sample 1 (fivefold pre-concentrated 0.2
respectively)
0
200000
400000
600000
800000
1000000
1200000
1400000
0 100 200 300 400 500 600 700time, s
88Sr
+ io
n in
tens
ity, c
ps
0
2
4
6
810
12
14
16
18
20
ion
inte
nsity
on
m/z
90,
cps
Sr-88
B
ion intensity on m/z 90
88Sr+
sample 1 50 ppq
90Sr
100 ppq 90Sr
200 ppq 90Sr
BprBpr Bpr Bpr Bpr
81
the influence of these effects on the accuracy of the measurements was considered to be
minimized. All results of the measurements are summarized in Table 7.4.3.
90Table 7.4.3. Sr concentration in analyzed ground water samples measured by ICP-SFMS and β-spectrometry
90Sr, concentration, fg ml-1
ICP-SFMS β-spectrometry
Sam le 1 18 p .8±1.9 19.2±0.61
Sample 2 32.3±2.2 30.1±1.8
Sample 3 <2.2 1.31±0.01
Sample 4 18.0±3.1 16.5±1.2
he concentration of 90Sr in the ground water samples analyzed ranged from 18.0 fg ml-1 to 32.3
g ml-1 and that in sample 3 was below the procedural LOD.
le 7.4.3). The results obtained show
7.5. LA-ICP-MS as important ultrasensitive techniques for determination
of long lived radionuclides and their isotopic ratios in solid samples
Capability d
sam les. The different calibration and measurements strategy of LA-ICP-MS technique were
T
f
To further evaluate the developed method, comparative determination of radioactive 90Sr in the
samples analyzed was performed by β-spectrometry (see Tab
a good agreement between the two spectrometric techniques. The precision of the analytical data
is slightly better using β-spectrometry. Whereas one hour is necessary for ICP-MS measurements
for 90Sr determination, the β-spectrometric measurement needs 3 days.
of LA-ICP-MS was evaluated for ultrasensitive radionuclide analysis in various soli
p
applied for this purpose.
82
7.5.1. Determination of U isotopic ratio on the surface of biological samples using
cooled LA chamber for LA-ICP-MS
An analytical p determination of precise uranium isotope
tios on a thin uranium layer on a biological surface by laser ablation inductively coupled
ser crater diameter (down to 5μm) can be obtained with the
g 7.5.1. Dried droplet of CCLU 500 isotopic standard reference material deposited onto flower leaf and craters of
ifferent diameters produced on the leaf under optimized conditions of LA-ICP-MS..
rocedure has been proposed for the
ra
plasma sector field mass spectrometry (LA-ICP-MS). A cooled laser ablation chamber using a
Peltier element was developed in order to analyze element distribution in thin cross sections of
frozen tissues with a lateral resolution in the µm range. In order to study the figures of merit of
LA-ICP-MS with the cooled laser ablation chamber, one drop (20 µl, U concentration 200 ng
mL-1) each of the certified isotope reference materials NIST U350 and U930, the uranium
isotopic standard CCLU 500 and also a drop of uranium with a natural isotopic pattern was
deposited and analyzed on the biological surface (flower leaf). For mass bias correction on the
surface of the flower leaf one droplet of isotopic standard reference material NIST U-020 (20 µL,
uranium concentration 100 ng mL-1) was added. After the drying in the heating oven (T=75ºC,
2h), the sample was analyzed by LA-ICP-SFMS using the cooled laser ablation chamber
developed in this experiment.
Relatively high laser power density (3.3×109 W cm2) – in order to avoid fractionation effects - in
connection with the small la
“Ablascope” laser ablation system. As an example, In Fig 7.5.1.a and b, the dried droplet of
CCLU 500 and the laser craters generated on it under optimized ablation conditions are shown.
Fi
d
a) b)
10μm
500μm
Diameter of laser crater
50μm25μm 15μm
83
The laser produces well-defined craters of 10, 15, 25 and 50 μm if the laser beam is focused on
e sample surface. Variation of the laser beam diameter has a direct influence on the amount of
aterial if the sample surface was scanned. Since the energy density of the laser remains
andard
lution (20 μl, U concentration 100 ng mL-1) deposited onto the flower leaf
ion of the developed LA-ICP-MS procedure for uranium isotope ratio
easurements was studied using NIST U-350, NIST U930 and CCLU-500 uranium isotope
reference materials as well as uranium with natural isotopic composition (see Table 7.5.1 and Fig
7.5.3a,b.
th
ablated m
constant it can be expected that the laser crater size is directly related to the intensity. Fig 7.5.2
shows the dependence of the 238U+ ion intensity signal on the different size of the focused laser
beam, measured on the dried droplet of natural uranium solution on flower leaf surface.
A good correlation between the measured ion intensity of 238U+ and the diameter of the laser
crater (i.e. the amount of ablated material) of the analyzed sample was determined.
If a substantial amount of material is transported into the plasma, it may cause a change in the
plasma conditions and would result in a reduction of the ionization efficiency. In our experiment,
the dependence of laser crater diameters does correlate to the intensity of the peaks, and,
therefore, will not affect the accuracy of the measurements with varying laser beam size.
Fig 7.5.2. Dependence of 238U+ ion intensity signal on the spot size (100 laser shots, repetition frequency 20 Hz)
measured by LA-ICP-MS with cooled laser ablation chamber on the dried droplet of natural uranium st
so
160000
180000
0
20000
40000
60000
80000
100000
120000
140000
0 50 100 150 200 250 300Time, s
238 U
+ ion
inte
nsity
, cps
10μm 15μm
25μm
50μm
The accuracy and precis
m
84
Table 7.5.1. Precision and accuracy of uranium isotope ratio, measured in dried droplet of NIST U-350, NIST U930
and CCLU-500 uranium isotope reference materials using cooled and non-cooled ablation chamber.
*Measured isotopic ratio *RSD % *Accuracy % St dard
re rence
m
Isotopic Recommended
an
fe
aterial ratio 15μm 25μm 50 μm 15 μm 25 μm 50 μm 15 μm 25 μm 50 μm isotopic ratio
Non-cooled laser ablation chamber 234U/238U
236
0.00325
0.50
0.
0.00340
0.
0.00350
982
0
9.4
6.3
8.2 8.1
5.9
16.1
7.2
12.3 10.0 0.00387 235U/238U
U/238U
714 0.50768 0.57
00286 00284 .00281 7.9
6.1
7.3 6.9
7.1 -6.1
-10.2 -9.4 -8.0
0.54648
0.00259
NIST
U350
NIST
U930
234U/238U 235U/238U
0.17886
15.63
0.17906
15.9
0.18207 10.7 9.2 9.0 11.0
9.9
10.9
8.2
9.4
8.2
0.20097
17.34 236U/238U 0.04103
2 15.92 5.1 4.9 4.5
0.04091 0.04069 9.9 9.8 9.0 -8.9 -8.6 -8.0 0.01112
C
500
CLU-234U/238U 235U/238U 236U/238U
0.00946
0.89792
0.00313
0.00966
0.90091
0.00268
0.00971
0.90191
0.00302
12.7
5.7
5.5
9.7
5.5
5.2
8.3
4.0
5.0
14.9
10.2
-12.1
13.1
9.9
3.9
12.7
9.8
-8.2
0.01112
0.99991
0.00278
Coole bl ch er d laser a ation amb
NIST
U350
234U/238U 235U/238U 236U/238U
0.00372
0.5344
0.00272
0.00369
0.5366
0.00265
0.00276
0.5524
0.00252
2.0
1.3
2.1
1.6
1.2
2.0
1.4
0.9
1.9
4.2
2.2
-4.8
4.7
1.8
-2.1
3.2
-1.1
3.2
0.00387
0.54649
0.00259
NIST
U930 235U/238U 17.07 17.19 4 1.6 0.9 0.8 17.34
234U/238U
236U/238U
0.19453
0.03851
0.19494
0.03715
0.19594
17.21 1.0 0.8 0.
0.03809
1.8
1.5
1.6
1.3
1.1
1.0
3.2
-2.2
3.0
1.4
2.5
-1.1
0.20097
0.01112
CCLU-
500
234U/238U 235U/238U 236U/238U
0.01083
0.9889
0.00285
0.01137
0.9909
0.00284
0.01124
1.0049
0.00276
1.5
1.3
1.4
2.0
1.2
2.0
1.6
0.9
1.6
2.6
1.1
-2.4
-2.2
0.9
-2.1
-1.1
-0.5
1.2
0.01112
0.99991
0.00278
*15μm;25 5 – ater d
μm; 0μm laser cr iameter
85
Fig. 7.5.3a. Precision of 234U/238U and 235U/238U isotope ratios, measured by LA-ICP-MS in dried droplet of uranium
with natural isotopic composition using cooled and non-cooled laser ablation chamber.
02468
101214161820
15 μm 25 μm 50 μm 15 μm 25 μm 50 μmdiameter of ablated crater
RSD
, %
non-cooled Cooled234U/238U
235U/238U
cooled
Fig 7.5.3b. Accuracy of 234U/238U and 235U/238U isotope ratios, measured in dried droplet of uranium with natural
isotopic composition by LA-ICP-MS using cooled and non-cooled ablation chamber.
0
2
4
6
8
10
12
14
16
15 μm 25 μm 50 μm 15 μm 25 μm 50 μmdiameter of ablated crater
Acc
urac
y, %
non-cooled Cooled234U/238U
235U/238U
cooled
An improvement of analytical results was observed when the ablation chamber of the laser
ablation system was cooled to about -15ºC (see Table 7.5.1). The accuracy and precision in all
measured samples were up to one order of magnitude better than in the case of the non-cooled
86
LA chamber. For the measured uranium isotopic standards, for instance, precision for 235U/238U
isotopic ratio with 50 μm spot size ranged from 0.4 - 0.9% RSD, whereas accuracies were in the
range of 0.5 – 1.1%. For the uranium with natural isotopic composition (see Fig 7.5.3a, b) the
best precision and accuracy were also achieved for 235U/238U isotopic ratio with 50 μm laser
crater diameter and found to be 0.9 and -0.2%, respectively. The same behavior for precision and
accuracy was observed in 234U/238U isotopic ratios, which for cooled LA chamber (50 μm laser
crater) were 3.2% and 1.8% in comparison to the non-cooled LA chamber with 11.0% and 8.8%,
respectively.
The most probable reason for this improvement in precision and accuracy is that in the case of the
non-cooled LA chamber (or non-cooled analyzed sample) the water vapor produced during the
laser ablation of biological sample (flower leaf) is very difficult to control and will lead to
changes in the plasma condition and ionization efficiency. However, when the ablated sample is
cooled, these vapors have less effect on the plasma and, therefore, result in increased precision
and accuracy. In addition, the adsorption properties of the laser energy in ice are significantly
better than in water matrix, which would also leads to improvements in the precision and
accuracy of the measurements.
7.5.2. Application of solution based calibration LA-ICP-MS for determination of
actinide as well as other elements in NIST 612 glass standard reference
material.
Microconcentric nebulizer DS-5, was directly assembled to the laser ablation cell (see Fig. 6.4),
and was used for introduction of calibrated solution during the LA-ICP-MS measurements.
Application of such solution based calibration arrangements were carried out in order to perform
standard addition calibration procedure for multielemental ICP-MS analysis of NIST 612 glass
standard reference material. Laboratory prepared liquid standard solutions of selected elements
(Cu, Rb, Sr, Ar, In, La, Ce, Eu, Gd, Yb, Th and U) with the concentration of 50 pg ml-1, 100 pg
ml-1 and 200 pg ml-1 (further called LS-50ppt, LS-100ppt and LS-200 ppt respectively) were
nebulized simultaneously with the ablation of NIST 612 standard. Typical LA-ICP-MS spectra
(e.g for 107Ag+, 139La+, 157Gd+ and 172Yb+) with the nebulization of LS-50 ppt are presented in
Figs 7.5.5.
87
Fig. 7.5.5.. Typical ICP-MS spectra for 107Ag+, 139La+, 157Gd+ and 172Yb+ observed during ablation of NIST 612 using line scan method and simultaneous nebulization of 50 pg ml-1 laboratory synthetic standard solution of element of interest.
0
10000
20000
30000
40000
50000
60000
0 20 40 60 80time, s
ion
inte
nsity
, cps
0
2000
4000
6000
8000
10000
0 20 40 60 8time, s
ion
inte
nsity
, cps
0
0
2000
4000
6000
8000
10000
0 20 40 60 80time, s
ion
inte
nsity
, cps
0
10000
20000
30000
40000
50000
60000
0 20 40 60 80time, s
ion
inte
nsity
, cps
107Ag+ 139La+
157Gd+ 172Yb+
As can be see from the figure the relatively unstable signal is obtained during the ablation of
NIST 612 was obtained, that could be explained by the inhomogeneity of the sample as well as
instability of the laser beam. It should be noted here, the instability of the signals can be also
introduced by the measurements setting of ICP-MS data collecting. In the current experiments
only one pass per peak was used in order to reduce the time per complete LA-ICP-MS run.
To improve the stability of measurements, the obtained LA-ICP-MS signals were normalized to
the 107Ag+ ion intensity, as shown in Figure 7.5.6. Using such method, reasonably stable signals
were observed for all measured spectra.
The similar normalization to 107Ar+ was also applied during the evaluation of the LA-ICP-MS
measurements of NIST 612 glass standard and nebulization of LS-100 ppt, LS-200 ppt as well as
2% of MilliQ water.
88
Fig. 7.5.6. Normalized on measured 107Ag+ ion intensity ICP-MS spectra of the ablation of NIST 612 using line scan
method and simultaneous nebulization of laboratory synthetic standard solution of 50 pg ml-1.
01000200030004000500060007000
0 20 40 60 80time, s
ion
inte
nsity
, cps
0
1000
2000
3000
4000
5000
6000
0 20 40 60 8time, s
ion
inte
nsity
, cps
0
0
10000
20000
30000
40000
50000
0 20 40 60 80time, s
ion
inte
nsity
, cps
139La+ 157Gd+
172Yb+
Obtained results show a good correlation between the measured standards as well as the
relatively stable signal response. For instance, the normalized spectra for 88Sr+, 139La+ and 238U+
are presented in Fig. 7.5.7.
Fig. 7.5.7. LA-ICP-MS spectra of 88Sr+, 139La+ and 238U+ measured during ablation of NIST612 isotopic standard and
simultaneous nebulization of 2% HNO3, LS-50 ppt, LS-100 ppt and LS-200 ppt, respectively
0
10000
20000
30000
40000
50000
60000
70000
0 20 40 60 80time, s
139 La
+ ion
inte
nsity
, cps
LA of NIST612 & Blank
LA of NIST612 & LS-50ppt
LA of NIST612 & LS-100ppt
LA of NIST612 & LS-200ppt
0
10000
20000
30000
40000
50000
60000
70000
0 10 20 30 40 50 60 70 80
time, s
238 U
+ ion
inte
nsity
, cps
LA of NIST612 & Blank
LA of NIST612 & LS-50ppt
LA of NIST612 & LS-100ppt
LA of NIST612 & LS-200ppt
0
10000
20000
30000
40000
50000
60000
70000
0 10 20 30 40 50 60 70 80time, s
88Sr
+ ion
inte
nsity
, cps
LA of NIST612 & Blank
LA of NIST612 & LS-50ppt
LA of NIST612 & LS-100ppt
LA of NIST612 & LS-200ppt
LA started LA stopped LA started LA stopped
89LA started LA stopped
In the Figure 7.5.8 the ion intensity signals for all element of interest measured by the developed
LA-ICP-MS procedure are summarized. Obtained correlation factors R2 were determined to be in
the range of 0.9464 to 0.9999 (see also Table 7.5.5).
Based on these data the calibration curves were plotted and used for calculation of concentration
of measured elements. The regression line of obtained dependence was extended to the
intersection with the x-axis as depicted in the Figure 7.5.9, whereby the unknown concentration
in the measured NIST 612 was found.
Determined in such way concentration for 88Sr+, 139La+ and 238U+ were 238 pg ml-1, 130 pg ml-1
and 141 pg ml-1, respectively.
Fig. 7.5.8. Ion intensity signals of selected element observed during LA-ICP-MS measurements of NIST612 isotopic standard and simultaneous nebulization of 2% HNO3, LS-50 ppt, LS-100 ppt and LS-200 ppt, respectively
0
10000
20000
30000
40000
50000
60000
70000
Cu-63 Rb-85 Sr-88 Ag-107 In-115 La-139 Ce-140 Eu-153 Gd-157 Yb-172 Th-232 U-238
ion
inte
nsity
, cps
LA of NIST612 & BlankLA of NIST612 & LS-50pptLA of NIST612 & LS-100pptLA of NIST612 & LS-200ppt
90
Fig. 7.5.9 . Calibration curves for 88Sr+, 139La+ and 238U+, respectively, observed during LA-ICP-MS measurements of NIST612 isotopic standard and simultaneous nebulization of 2% HNO3, LS-50 ppt, LS-100 ppt and LS-200 ppt.
Taking into consideration difference in atomization efficiency of nebulizer and laser ablation
process, calculated concentration values were further corrected with the known Ag concentration
(as internal standard) in the NIST 612. Table 7.5.5 summarizes the all calculated element
concentrations in NIST 612 glass standard determined by developed LA-ICP-MS procedure as
well as their certified values.
Table 7.5.5.Calculated concentration in NIST 612 measured by developed LA-ICP-MS procedure
Concentration R2 NIST612uncor,
pg ml-1NIST612cor,
ng ml-1NIST612cert,
ng ml-1
Accuracy, %
Cu 0.9464 132.6 35.9 37.7 4.8 Rb 0.9964 119.4 32.3 31.4 -2.9 Sr 0.9932 283.3 76.7 78.4 2.2 Ag 0.9999 81.3 22.0 22 - In 0.9719 73.6 19.9 - - La 0.9941 130.2 36.9 36 -2.5 Ce 0.9759 152.8 41.4 39 -6.04 Eu 0.9932 126.0 34.1 36 5.3 Gd 0.9828 149.6 40.5 39 -3.8 Yb 0.9959 161.6 43.7 42 -4.1 Th 0.9813 134.2 36.3 37.8 3.9 U 0.9958 141.5 38.3 37.3 -2.6
R2 = 0.9958
-60000
-40000
-20000
0
20000
40000
60000
80000
-500 -400 -300 -200 -100 0 100 200 300
U238 (LR)Linear (U238 (LR))
141 pg ml-1
R2 = 0.9932
-20000
-10000
0
10000
20000
30000
40000
50000
60000
-500 -400 -300 -200 -100 0 100 200 300
Sr88 (LR)Linear (Sr88 (LR))
283 pg ml-1
R2 = 0.9941
-60000
-40000
-20000
0
20000
40000
60000
80000
-500 -400 -300 -200 -100 0 100 200 300
La139 (LR)Linear (La139 (LR))
130 pg ml-1
91
The results show an excellent agreement between the obtained and certified data – the accuracies
of the measurements were ranged from 2.2% to 6.04% for all measured elements, when the Ag
was used as the internal standard.
Using the developed procedure determination of other element can be also possible in the
measured NIST 612 reference material. For, instance, the indium concentration was calculated to
be 19.9 ng ml-1, although it was not certified in the analyzed standard.
7.5.3. Determination of U and Th by ID-LA-ICP-MS in faeces samples
A new analytical procedure for actinide determination in human faeces samples was developed
using Isotope Dilution LA-ICP-MS method.
Ashed faeces sample was divided into two parts. The one of these parts was used as the reference
one, and was spiked with the 0.5 ng ml-1 of liquid uranium standard reference material NIST
U930, properly mixed and dried in the heating oven. Than the both faeces samples were placed
onto the target holder and were used for LA-ICP-MS measurements of 232Th as well as 235U/238U
isotopic ratio (see Figs 7.5.10 a.b)
Fig 7.5.10. Measured by LA-ICP-MS 235U/238U isotopic ratios and 232Th ion intensity, respectively, in a) unspiked faeces sample; b) spiked with NIST U930 faeces sample
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
0 20 40 60 80 100 120 140 160 180 200
time, s
235 U
/238 U
isot
opic
ratio
U-235/U-238
a)
0500
1000150020002500300035004000
0 50 100 150 200
time, s
232 T
h io
n in
tens
ity
Th-232
b)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 20 40 60 80 100 120 140 160 180 200
time, s
235 U
/238 U
isot
opic
ratio U-235/U-238
0500
1000150020002500300035004000
0 50 100 150 200
time, s
232 T
h io
n in
tens
ity
Th232(uncor)
92
The 235U/238U isotopic ratios in the unspiked and spiked samples were determined to be 0.00716
and 0.13582, respectively. Using these data the uranium concentration in the faeces sample were
calculated to be 69.5 ng g-1, using the isotope dilution formula 7.5.1
( ) ( )[ ]( )TsTs mmSXXTCC // −−= (7.5.1)
where
Cs and CT – concentration of uranium in the sample and tracer, respectively;
T, X, S – 235U/238U isotopic ratios in the tracer, spiked sample (mixture) and
unspiked sample, respectively;
ms and mT are the relative atomic masses in the sample and tracer, respectively.
The obtained concentration of uranium was further applied as internal standard in order to
determine the thorium content in faeces. Taking into consideration that the difference in ion
intensity for laser ablation of the sample and nebulization of U standard using DS-5 nebulizer
were about 1776, the thorium concentration in analyzed faeces sample of 52 ng g-1 were
calculated.
For quality assurance of the developed ID-LA-ICP-MS method, analyzed faeces sample was
microwave digested and measured by ICP-MS. Obtained values for U and Th concentration in
the faeces were 72.2±3.0ng g-1 and 55.1±2.1 ng g-1, respectively, that is in a good agreement with
the measured ID-LA-ICP-MS data.
7.6. Application of LA-ICP-MS for determination of actinide as well as
other elements in single proteins separated by 2D gel electrophoresis
A new analytical technique was developed for LA-ICP-MS determination of uranium, thorium as
well as other elements in human proteins prior separated in two-dimensional gels using
93
electrophoresis. Fig 7.6.1. shows the example of 2D electropherogam (silver staining) of
separated protein with the schematic view of scanned procedure. The region of interest with the
marked in the 2Dgel was cutted (in the figure see cut 1 and cut 2) into the small sections that
were used for the LA-ICP-MS measurements. 200 laser shots per spot were used to collect the
information about the content of selected element in measured protein.
In the Fig 7.6.2. the LA-ICP-MS spectra of U ion intensity measurements in two selected 2D gel
sections (cut-1 and cut-2) is presented. Before the measurements of ion intensity in protein spots,
the blank value (in the gel region free from protein) was determined. To ensure the measured data
each protein spot was analyzed three times in different places.
Fig 7.6.1. 2D electropherogam of separated protein with the schematic view of scanned procedure
6
14.
M.W.
pI 4 pl 7
As shown in the Figure 7.6.2a no uranium was detected in the spots 1a and 1b – the ion intensity
in these spots were comparable to the blank intensity. In contrast to this, the increasing of the
uranium signal was observed (about 4-5 time of the peak area) in the spot 1c of the same cut.
1 1a
2 2a 2b
B
1b
1c B
94
Similar increasing of the uranium signal in comparison to the blank intensity was also found in
spots 2a and 2b of the Cut-2 (see Fig. 7.6.2b). Fig 7.6.2. LA-ICP-MS transient signals of uranium measured in selected protein spots of : a) Cut 1 and b) Cut-2 gel
he thorium LA-ICP-MS measurements in the same proteins spots of Cut-1 and Cut-2 is
sections, respectively a)
b)
050
100150200250300350400450500
0 100 200 300 400 500Time, s
238 U
ion
inte
nsity
Blank Spot 1a
Spot 1b
Spot 1c U 238
0
50
100
150
200
250
300
0 50 100 150 200 250 300 350 400Time, s
238 U
ion
inte
nsti
U-238
T
presented in Figs 7.6.3a and b, respectively. Comparing to the uranium measurements, the 232Th+
ion intensity signal was about the same in the gel blank and measured protein spots.
y
Gel blank
Spot 2a Spot 2b
95
Fig 7.6.3. . LA-ICP-MS transient signals of thorium measured in selected protein spots of : a) Cut 1 and b) Cut-2 gel
sections, respectively.
020406080
100120140160180
0 100 200 300 400 500Time, s
232T
h io
n in
tens
tiy
Th-232
Gel blank
Spot 1a
Spot 1b
Spot 1c
0
20
40
60
80
100
120
140
160
0 50 100 150 200 250 300 350 400Time, s
232 Th
ion
inte
nstiy
Th-232
Gel blank Spot 2a
Spot 2b
Using developed procedure a very fast screening by LA-ICP-MS was possible. For instance, 176
separated proteins were measured in 3 hours for its U, P, S, Cu and Zn content in another 2D gel
(other sample) (see Fig. 7.6.4).
96
Fig 7.6.4. 2D electroferogram of separated proteins of human brain tissue as well as schematic arrangement of scanned protein spots
pI 4 7
Brain sample 7#99 (non AD, 1mg/ml)
1 b c fde
j
a
2a
np o
b c dk l
m
fe j
B
B
B
B
a bс d e f
j k
l
n mop
qr
B
f l m
nrs
a b c d
j
q p
e k
o
a e
f
Bjl
o
b cd
k
n m
43
5
a b c d ef j
onmlk
BBn
b c
k
l
p
ejm
fo
daB
67
s
j
ef d
lk
a bc
nm o
p q r
BB
8 f
jm
q
a b c d
lno
pB
e
9 k
b
a
cd
e f
j
m
n
kl
op
qrs
B
10a
b
c de
lnm
k j
f
B
11
a
bc
lj
d
k
f
e12B
fe
c
a l
mk
j
n
o
b
B
d
13
B
l
j
m
k
f e
dc
a
b
14
pI 4 7
Brain sample 7#99 (non AD, 1mg/ml)
1 b c fde
j
a
2a
np o
b c dk l
m
fe j
BB
B
B
B
a bс d e f
j k
l
n mop
qr
B
f l m
nrs
a b c d
j
q p
e k
o
a e
f
Bjl
o
b cd
k
n m
43
5
a b c d ef j
onmlk
BBBn
b c
k
l
p
ejm
fo
daB
67
s
j
ef d
lk
a bc
nm o
p q r
BBB
8 f
jm
q
a b c d
lno
pB
e
9 k
b
a
cd
e f
j
m
n
kl
op
qrs
B
10a
b
c de
lnm
k j
f
B
11
a
bc
lj
d
k
f
e12B
fe
c
a l
mk
j
n
o
b
B
d
13
B
l
j
m
k
f e
dc
a
b
14
The typical LA-ICP-MS spectra for e.g. Cut-13 are shown in Fig 7.6.5. From this data a
qualitative only qualitative analysis is possible, whereby, for example, uranium was clearly
detected in protein spots 13c, 13k and 13l.
97
Fig. 7.6.5. LA-ICP-MS transient signals of selected elements measured by developed procedure in protein spots of Cut-13
0
1000
2000
3000
4000
5000
6000
7000
8000
0 50 100 150 200 250 300 350
Zn64 (MR)
0
500
1000
1500
2000
2500
0 50 100 150 200 250 300 350
P31 (MR)
0
200
400
600
800
1000
1200
0 50 100 150 200 250 300 350
U238 (MR)
0
1000
2000
3000
4000
5000
6000
0 50 100 150 200 250 300 350
Cu63 (MR)
Ion intensity [cps]
Ion intensity [cps]
Ion intensity [cps]
Ion intensity [cps]
31P+ 63Cu+
64Zn+ 238U+
Blank
Blank
Blank
Blank
13c
13c
13c
13c
13l 13l
13l 13l
13k
In order to determine the concentration of measured elements the quantification algorithm was
developed that utilize the combination of LA-ICP-MS with high-resolution MALDI-FTICR-MS
(matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass
spectrometry) measurements. For such quantification procedure of selected elements in proteins,
sulfur was chosen as an internal standard element. The amount of sulfur in protein of interest was
determined from analyzing the sequence of protein by MALDI-FTICR-MS (see Fig 7.6.6 as well
as Table 7.6.1).
98
Fig 7.6.6.MALDI-FTICR-MS mass spectrum of protein spot 5a with identified peptides
Table 7.6.1. MALDI-FTICR-MS identified proteins (with number of Sulfur atoms) as well as calculated concentration of P, S, Cu, Zn and U from the LA-ICP-MS measurements
Concentration , mg/g spot Protein Weight
M.W
Number
of S-
atoms
P-
lation P S Cu Zn U
3n AINX_HUMAN Alpha-
internexin
55528 6 3 0.05 3.4 38.6 2.2 0.001
4n KCRB_HUMAN Creatine
kinase
42644 16 2 0.04 12 <LOD <LOD <LOD
3f VAA1_HUMAN
Vacuolar ATP
68304 29 5 0.06 13.5 <LOD 8.8 0.05
5a VAB2_HUMAN Vacuolar
ATP
56500 22 6 0.09 12.4 220 43.5 0.06
2l TBB4_HUMAN Tubulin
beta-4 chain
50432 27 6 0.12 17.1 180 42 <LOD
2f TBA1_HUMAN Tubulin
alpha-1 chain
50151 22 64 1.27 14 159 49 <LOD
99
Using this value the concentration of the measured elements were determined by the formula
7.6.1
( )( )[ ]( ){ } ssp
xg
xg
xg
sgsp
xsp
xsp CCCIIIIC
s///= 7.6.1
where
spCx and spCs concentration of element of interest and Sulfur in protein spot,
respectively
gCx and gCs concentration of element of interest and Sulfur in gel blank,
respectively (were determined by microwave digestion of gel blank and direct
ICP-SFSM measurements) spIxand spIs ion intensity of element of interest and Sulfur in protein spot,
respectively gIx and gIs ion intensity of element of interest and Sulfur in protein spot,
respectively
The results of calculated concentration of selected elements in identified protein sots are
summarized in Table 7.6.1. The Uranium was detected in protein spots 3n, 3f and 5a in the
concentration of about 1, 5 and 6 ng g-1. In other identified protein spots, the uranium was below
the detection limit (see Table 7.6.2) and therefore was not detected. The precision of the
measurements were about 30%.
Table 7.6.2.Limits of detection for selected elements calculated for developed LA-ICP-MS measurements of separated by 2D gel electrophoresis proteins
Element LOD, μg g-1
P 0.7
S 2407
Cu 82
Zn 53
U 0.01
100
Future work will be of interest in order to improve the screening technique using a laser
ablation system with better lateral resolution and development of further quantification
procedures especially for proteins which do not contain sulfur.
7.7. Lateral distribution of concentrations of actinides as well as some
other elements in thin cross section of brain tissue measured by LA-
ICP-MS
The aim of the present experiments was to develop a new microanalytical technique using LA-
ICP-MS for the simultaneous and quantitative determination of element distribution in thin
sections of human brain tissues. The results on selected sections of brain tissue measured by LA-
ICP-MS will provide extremely important information on the lateral and depth element
distribution of essential and toxic elements in brain samples (e.g., of patients in comparison to
healthy control tissues).
The application of LA-ICP-MS in order to study the lateral distribution of U and Th, as well as
other elements in the thin cross section human brain samples was evaluated during the present
Ph.D. work. In the following paragraphs the detailed description of the observed results are
discussed.
7.7.1. Human brain samples
7.7.1.1. Hippocampus region
An analytical LA-ICP-MS procedure was developed to produce images of element distribution in
20μm thin section of human brain tissue (hippocampus region). The Cresyl violet stained view of
the hippocampus region with the marked layers is shown in Fig. 7.7.1. The sample surface was
scanned (raster area 20 mm x 4 mm) with a focused laser beam (wavelength - 213 nm; diameter
of laser crater – 50 µm and laser power density - 3 . 109 W cm-2) in a cooled laser ablation
chamber developed for these measurements.
101
In order to obtain two-dimensional imaging of element distribution, the region of interest (see
Fig. 7.7.2c) was systematically screened (line by line) using a focused laser beam. In Fig. 7.7.2 a
and 7.7.2b the ion intensities profile of uranium and thorium, respectively, in thin sections of
hippocampal tissue measured by LA-ICP-MS are represented. The figures show that, generally,
homogeneous distribution was found for the measured actinides. In compare to this, Figs. 7.7.3a and 7.7.3b demonstrate the two-dimensional representation of the
distribution of zinc and copper, respectively, in the analyzed hippocampus. As expected for zinc,
which has been demonstrated in mossy fibre synapses by Danscher et al[123]., highest
concentration of zinc was found in the hilus region and lucidum layer, i.e. the target of the mossy
fibres. In contrast, copper (Fig. 7.7.3b) reaches only relative low ion intensity in this region, but
much higher ion intensities (and, therefore, higher concentrations) were observed in the stratum
lacunosum molecular layers of the Cornu Ammonis (see Fig. 7.7.1).
Fig.7.7.1. Cresyl violet staining of cell bodies of brain hippocampus with the structure regions.
Lucidum layer = layer of interest
Artifact
oriens layer
pyramidal layer
radiatum layer
lacunosum-molecular layer
1
32
1= molecular layer
2= granular layer
3= hilus
102
Fig. 7.7.2 Element distribution a) of thorium and b) uranium measured by LA-ICP-MS in human hippocampus. Measured ion intensities are shown. hippocampus c) Histologically processed brain tissue in which cell bodies were stained in order to demonstrate the layered structure of the analyzed region.
0 2 4 6 8 10 12 14 16 18 20 length, mm
0 1 2 3 4
wid
th, ,
mm
w
idth
, ,m
m
10 12 14
ion intensity, cps
0 2 4 6 8 10 12 14 16 18
0 1 2 3 4 w
idth
, ,m
m
length, mm
10 12 14
ion intensity, cps
0 2 4 6 8 10 12 14 16 18
0 1 2 3 4
length, mm
a)
b) c)
The quantification of analytical data was performed via measuring of prepared synthetic matrix-
matched laboratory standards with well-defined element concentrations under the same
experimental conditions as analyzed samples (see Fig. 6.11). Prepared three slices of the same
brain tissue spiked with selected standard solutions (concentrations of Cu and Zn in brain tissue
were 10, 5, 1 µg g-1 and of Th and U were 0.1, 0.05, 0.01 µg g-1 ) were analyzed by LA-ICP-MS.
Figs. 7.7.4.a and 7.7.4b show the distribution patterns of zinc and copper in the human
hippocampus as measured in by LA-ICP-MS. The layered distribution pattern of both elements is
clearly visible. The zinc concentration (Fig. 7.7.4a) in the investigated brain sample is mostly
lower than 5 µg g-1.
103
Fig. 7.7.3 Element distribution a) of zinc and b) cupfur measured by LA-ICP-MS in human hippocampus. Measured ion intensities are shown. hippocampus c) Histologically processed brain tissue in which cell bodies were stained in order to demonstrate the layered structure of the analyzed region.
0 2 4 6 8 10 12 14 16 18 20
length, mm
0 1 2 3 4
wid
th, ,
mm
10 12 14
ion intensity, cps
0 2 4 6 8 10 12 14 16 18
0 1 2 3 4
wid
th, ,
mm
length, mm
10 12 14
ion intensity, cps
0 2 4 6 8 10 12 14 16 18
0 1 2 3 4
wid
th, ,
mm
length, mm
a)
b)
c)
The maximal zinc concentration (10 µg g-1) is restricted to a small region of the hippocampus (in
the hilus region and lucidum layer). Copper (Fig. 7.7.4b) was found in higher overall
concentrations (maximum: 14 µg g-1) in the hippocampus. Furthermore, it was not only present in
discrete concentrations the hilus, but also in higher concentrations in the pyramidal and
lacunosum-molecular layers of the Cornu Ammonis.
104
Figs.7.7.4 Concentration profile a) of zinc and b) copper measured by LA-ICP-MS in human hippocampus.
Calibration is performed via synthetic matrix-matched laboratory standards for 1, 5 and 10 ppm of analyte (see
inserted figures on left).
f interest are the findings of element distribution for the radioactive elements thorium and
10ppm
5ppm
1ppm
width, mm
length, mm
###
10ppm
5ppm
1ppm
width, mm
length, mm
Zn+
Cu+
O
uranium. In contrast to the layered structure of the examined essential elements (Fig. 7.7.4a and
7.7.4b), the thorium and uranium displayed a similar and relatively homogeneous profile in the
cross section of the hippocampus as revealed by microlocal measurements using LA-ICP-MS
(see Fig. 7.7.5a and 7.7.5b). The measured uranium and thorium concentration was slightly
higher than the detection limit. The detection limits of the microanalytical technique for Th and U
determination in thin sections of brain tissues using LA-ICP-MS were determined to be 10 ng g-1.
105
Figs.7.7.5 Concentration profile a) of thorium and b) uranium measured by LA-ICP-MS in human hippocampus.
Calibration is performed via synthetic matrix-matched laboratory standards for 10, 50 and 100 ppb of analyte (see
inserted figures on left).
U+0.1 ppm
0.05 ppm
0.01 ppm
length, mm
width, mm
Th+0.1 ppm
0.05 ppm
0.01 ppm
length, mm
width, mm
7.7.1.2. Analysis of brain cancer region
The developed LA-ICP-MS procedure was also applied for study the profile distribution of the
Cu, Zn, Pb and U in the human brain tissue affected with the Glioblastoma Multiforme [GBM]
(the one of the most frequent tumors of the central nervous system [124-126]. Prior to the
measurements identification of the tumor mass was performed, yielding a distinctive high cellular
area. Adjacent slices were labeled with tritiated receptor-ligands, like 3H-Pk11195 for peripheral
benzo-diazepinereceptor, that is only upregulated in the brain under pathological conditions) or
with 3H-CPFPX, a very specific ligand for A1 adenosine receptors[126, 127].
106
The whole experimental arrangements as well as the measurements procedure were similar to
those for LA-ICP-MS analysis of hippocampus (see section 7.7.1.1). The sample slice of 20μm
thickness was continuously scanned using “line scan method” of laser ablation. The measured ion
intensity was used to produced the two dimensional view of the concentration profile of selected
elements in analyzed human brain tissue.
The resulting 2D images for Zn, Cu and Pb profiles are depicted in Figs. 7.7.6.a and b,
respectively. In the Fig 7.7.6.d the autoradiograph of peripheral benzodiazepine receptor (pBR)
with 3H-Pk11195 with the clearly shown tumor area is presented. Obtained results for Zn, Cu and
Pb were similar, and, in general, were depleted in the tumor cells in comparison to the control
ones. The surprising in this experiment was the fact that, in spite to the high cell density found in
the tumor region, the lower concentration of measured elements was found.
High numbers of mitochondria per area can be expected with respect to the high cellular density
of tumors and prominent enzyme systems depend on copper and zinc such as matrix
metalloproteases, Cytochrome c-oxidase of the respiratory chain and phenol oxidases [126] The
copper levels seem to be low in tumors but correlate with the invasion zone of tumors and its
A1AR distribution. This result and its functional meaning has to be further investigated.
Zinc is known to be bound to many enzymatic systems, like alcohol-dehydrogenase (ADH,
substrate binding), carbon anhydrase and within some proteases. Furthermore, insulin binds zinc.
Here, we found reasonable low amounts of zinc, that is- with respect to the high cellular density
as shown in Fig. 7.7.6d- surprising as well. It has been shown, that the tumor-suppressor-protein
p53-translocation into the nucleus is also dependent upon zinc. Here, besides possible mutations
within the p53 protein, a simple explanation of the p53 dysfunction could be, that there is no zinc,
keeping the p53 more in the cytosolic compartment rather than beeing translocated into the
nucleus [127, 128].
107
Figs. 7.7.5 2D images of ion intensity profile of a) copper and b) zinc measured by LA-ICP-MS in the human brain samples affected with GBM; c) autoradiograph of peripheral benzodiazepine receptor (pBR) with 3H-Pk11195.
a) b) Zn+
Cu+
c)
The element distributions were obtained for lead and uranium intensity profiles (see Figs 7.7.6).
Measured distributions were comparable to those obtained for Cu and Zn, whereby the depletion
of Pb and U in comparison to the control tissue was clearly observed in the tumor cells. This
effect, however, needs to be further investigated as well.
108
Figs. 7.7.6 Images of ion intensity profile of a) lead and b) uranium measured by developed LA-ICP-MS method in
the human brain samples affected with GBM;
a) b)
Pb+ U+
The results from current LA-ICP-MS measurements might be of great interest for the further
understanding of basic mechanisms in tumors. Automatization of the technique can save time in
histological characterization of tumors. For instance, an automized LA-ICP-MS analysis of a
single slice for ions can be done in about six hours, whereas most IHC-stainings take longer.
109
8. Conclusions and outlines
Within the framework of present Ph.D. study it was demonstrated that inductively coupled
plasma mass spectrometry represent a powerful analytical technique and becomes a method of
choice for the determination of long lived radionuclides. The wide variety of developments
demonstrates significant improvements in the figures of merits of actinide as well as 90Sr
determination.
All procedures developed for the ideal solutions have been applied to real samples with the high
salt matrix consistence (e.g. urine sample, sea, ground water samples, etc).
The application of separation and co-precipitation techniques have shown to be adequate in order
to access the extremely low concentration of actinides. For instance, Pu in Sea of Galilee was
determined in 10-18 g ml-1 concentration level, after its pre-concentration from 100 L. The 240Pu/239Pu isotopic ratio of 0.17±0.05 were measured, which represents he value of
contamination of the Sea of Galilee due to the global fallout after nuclear weapon tests in the
sixties.
The limit of detection in for 239Pu in urine (after the pre-concentration from 1 L) was found to be
9×1018 and 1×1018 g ml-1, with the PFA-100 and DIHEN nebulizers, respectively.
To further improve the LOD of long lived radionuclides the nano-flow-injection ICP-MS
technique was developed. In these experiments the LODs for 238U and 242Pu of 230 000 and 38
000 atoms was achieved.
Moreover by application of some further methodical developments the additional improvements
of LOD for some actinide was achieved. For, instance, with the using of D2O water for the
dilution of the samples, the limits of detection for 236U determination can be improved about
order of magnitude, because of the formation of UD+ instead of UH+ molecular ions. The
minimum detectible ratio of 236U/238U was found to be 2×10-7 with the application for solution
introduction microconcentric nebulizer with membrane desolvator “Aridus”.
110
Significant progress has been achieved in the determination of 90Sr radionuclide by ICP-SFMS,
which half life time is equal 29 years. In the present study, the concentration of 90Sr in ground
water samples in the range of sub-fg ml-1 was determined, with the application of cold plasma
technique of ICP-SFMS as well as operating of mass spectrometer at medium mass resolution
mode.
The advantages of ICP-SFMS, as a multielemental analytical technique, have also be proved in
respect to the precise and accurate isotope ratio measurements. For example, the precision and
accuracy, yielded for the determined uranium isotopic ratios in the different standard reference
materials was ranged from 0.02 to 1.2 % and 0.001 to 2.5%, respectively.
For the direct analysis of the different kind of solid sample (biological or medical tissues, protein
spots, etc), the sample introduction into ICP-SFMS was performed by laser ablation. A cooled
laser ablation chamber (using two Peltier elements) was developed during the present study in
order to improve (up to one order of magnitude) the precision and accuracy of uranium isotopic
ratios in comparison to the non-cooled laser ablation chamber.
Furthermore, the application of LA-ICP-MS with cooled laser ablation chamber was successfully
established for microlocal analysis of element distribution in thin section of human brain tissue
samples (hippocampus and brain tumor regions). Two dimensional images of the concentration
profile of U, Th as well as Cu, Zn and Pb have been measured, that can provide to the specialist
further information about the biological and pathological processes inside the hippocampus or
brain tumor cells.
In future work, application of developed technique will be of great interest in order to determine
some other elements (such as P, S, Fe, Si etc) as well as to improve the lateral resolution of LA-
ICP-MS procedure (e.g. using the near-field effect in laser ablation).
111
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Acknowledgements
This work was carried out during the years 2002-2005 at the Central Division for Analytical
chemistry, Research Center Jülich, Germany.
I wish to express my deepest thanks to Dr.habil. J.S.Becker for her great support, interest and
valuable discussion. It was an honor to work with you.
I would like to thanks also to my “doctor-father” Prof. K. Volka, for his help and understanding
during the all stages of my Ph.D study.
I would like to thank Dr. P. Ostapczuk, for his great co-operation as well as for his help with the
all bureaucracy during my study in Jülich.
I wish to thank to Dr. S. Boulyga and Dr. C. Pickhardt, who introduced me to the ICP-MS and
LA-ICP-MS as well as adopted me to live in Jülich.
I thank to Mr. A. Izmer for his help and the nice time spent together.
My deepest thank to my girl fried and all my family for their great support
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10. List of publications 1. S.F.Boulyga, M.Zoriy, M.E.Ketterer, J.S. Becker
Depth profiling of Pu, 241Am and 137Cs in soils from southern Belarus measured by ICP-MS and α and γ spectrometry. J. Envir. Mon. 5(2003) 661-666.
2. M.V. Zoriy, A.Rashad, C.Pickhardt, H.T.Mohsen, H.Förstel, A.I. Helal, N.F. Zahran, J.S. Becker Routine method for 87Sr/86Sr isotope ratio measurements in biological and geological samples after trace matrix separation by ICP-MS Atom. Spectrom.24(6) (2003) 195-200.
3. J.S.Becker, M.V.Zoriy, U.Krause-Buchholz, J.Su. Becker, C.Pickhardt, M.Przybylski, W.Pompe, G.Rödel
In gel screening of phosphorus and copper, zinc and iron in proteins of yeast mitochondria by LA-ICP-MS and identification of protein structures by MADI-FT-ICR-MS after separation with two-dimensional gel electrophoresis J. Anal.At. Spectrom. 12 (2004), 1-9
4. J.Su.Becker, M.Zoriy, E.Damoc, M.Przybylski, J.S.Becker High resolution mass spectrometric brain proteimics combined with direct determination of elements (P, S, Cu, Zn, and Fe) by laser ablation inductively coupled plasma mass spectrometry: New methodology basis for unraveling key structures of neurodegeneration Nature Biotechnology. in preparation.
5. M.V. Zoriy, C.Pickhardt, P.Ostapczuk, R.Hille, J.S.Becker, Determination of Pu in urine at ultratrace levels by double focusing sector field inductively coupled plasma mass spectrometry Intrern. J. Mass Spectrom.232 (2004), 217-224
6. J.S.Becker, M.Zoriy, J.Su.Becker, C.Pickhardt, M.Przybylski Determination of phosphorus and metal in human brain proteins after isolation by gel electrophoresis by laser ablation inductively coupled plasma source mass spectrometry, J.Anal.At.Spectrom. 19 (2004) 1-5
7. M.V. Zoriy, L.Halicz, M.E.Ketterer, C.Pickhardt, I.Segal, P.Ostapczuk, J.S. Becker Reducing of UH+ formation for 236U/238U isotope ratio measurements at ultratrace level in double focusing sector field ICP-MS using D2O water as solvent J. Anal.At. Spectrom. 19 (2004) 363-367
8. A.P.Vonderheide, M.V. Zoriy, A.V. Izmer, C.Pickhardt, J.A. Caruso, P. Ostapczuk, R. Hille, J.S.Becker Determination of 90Sr at ultratrace levels in urine by ICP-MS J. Anal.At. Spectrom. 19 (2004) 675-680
9. J. S. Becker, M. Zoriy, L. Halicz, N. Teplyakov, I. Segal, C. Pickhardt and I. T. Platzner
Environmental monitoring of plutonium at ultratrace level in natural water (Sea of Galilee—Israel) by ICP-SFMS and MC-ICP-MS J.Anal.At.Spectrom 19, (2004), 1257–1261
10. Andrei V. Izmer, Sergei F. Boulyga, Myroslav V. Zoriy and J. Sabine Becker Improvement of the detection limit for determination of 129I in sediments by quadrupole inductively coupled plasma mass spectrometer with collision cell J.Anal.At.Spectrom 19, (2004), 1278–1280
11. Becker JS, Burow M, Zoriy MV, Pickhardt C, Ostapczuk P, Hille R,
Determination of uranium and thorium at trace and ultratrace levels in urine by laser ablation ICP-MS Atom. Spectrom. 25 (5) (2004) 197-202.
12. Pickhardt C, Zoriy M, Becker JS
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Metallornics and phosphoproteomics of 2D gels Nachrichten Aus Der Chemie 53 (1), (2005), 31-33.
13. J. Susanne Becker, Myroslav Zoriy, Carola Pickhardt, Michael Przybylski, J. Sabine Becker Investigation of Cu-, Zn- and Fe-containing human brain proteins using isotopic-enriched tracers by LA-ICP-MS and MALDI-FT-ICR-MS
Int. J. Mass Spec. 242 (2005) 135–144
14. Myroslav V. Zoriy, Peter Ostapczuk, Ludwik Halicz, Ralf Hille, J. Sabine Becker Determination of 90Sr and Pu isotopes in contaminated ground water samples by inductively coupled plasma mass spectrometry Int. J. Mass Spec. 242 (2005) 203–209
15. M.V. Zoriy, M. Kayser, A. Izmer, C. Pickhardt, J.S. Becker
Determination of uranium isotopic ratios in biological samples using laser ablation inductively coupled plasma double focusing sector field mass spectrometry with cooled ablation chamber Int. J. Mass Spec. 242 (2005) 297–302
16. Dirk Schaumloffel, Pierre Giusti, Myroslav V. Zoriy, Carola Pickhardt, Joanna Szpunar, Ryszard Lobinski
and J. Sabine Becker Ultratrace determination of uranium and plutonium by nano-volume flow injection double-focusing sector field inductively coupled plasma mass spectrometry (nFI–ICP-SFMS)
J.Anal.At.Spectrom 20, (2005), 17–21
17. Zoriy, M.V. Varga, Z, C. Pickhardt, P.Ostapczuk, R. Hille, L. Halicz and J. S. Becker Determination of Ra-226 at ultratrace level in mineral water samples by sector field inductively coupled plasma mass spectrometry J.Env. Mon, 7, (2005), 514-518
18. Becker JS, Zoriy MV, Pickhardt C, Palomero-Gallagher N, Zilles K Imaging of copper, zinc and other elements in thin section of human brain samples (Hippocampus) by laser ablation inductively coupled plasma mass spectrometry Analytica Chemistry, 77 (10), (2005), 3208-3216
19. Becker JS, Zoriy MV, Damoc, E., J.Su. Becker and M. Przybylski Determination of element concentration by LA-ICP-MS of Alzheimer’s Disease brain proteins combined with proteome Analysis by High Resolution FT-ICR-MS ICP Information Newsletter, 30 (10), (2005), 1046
20. Becker JS, Zoriy MV, Pickhardt C., J.Su. Becker and M. Przybylski Determination of Long-Lived Radionuclides by LA-ICP-MS ICP Information Newsletter, 30 (10), (2005), 1025
21. Izmer, A.V Zoriy, M.V. Pickhard, Quadakkers W, Shemet W, Singheiser L. and J. S. Becker LA-ICP-MS studies of cross section of NiCrAlY-based coatings on high-temperature alloys J. Anal. At. Spectrom, 20, (2005), 918-923
22. Becker JS, Zoriy MV, Dehnhardt M., Pickhardt C and Zilles Copper, zinc, phosphorus and sulfur distribution in thin section of rat brain tissues measured by laser ablation inductively coupledplasma mass spectrometry: possibility for small-size tumor analysis J. Anal. At. Spectrom, 20, (2005), 912
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