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July 8, 2014
1
Fred Fryer
Agilent Technologies
Use of an ICP-MS for direct analysis of multiple elements in a sample matrix > 0.4% dissolved solids using uHMI
Challenges of measuring samples
Weakly acidified water is our ideal and difference in response
compared to the ideal is undesirable or needs to be
compensated for.
Differences observed are:
Element signal suppression or enhancement (per sample)
Longer term upward or downward change in signal (drift).
The change is seen once the dissolved solid content of a
sample excedes 0.2% w/v and can have a few causes.
July 8, 2014
Confidentiality Label
3
Effects of the sample matrix
Sample density, surface tension, viscosity affects nebulisation
Intractable material deposits on the cooler interface and changes the performance of the vacuum interface (cones) and is seen as drift.
The major element composition in the plasma affects degree of ionisation eg: sodium suppresses, carbon enhances, at about 0.5% or more.
The composition of the ion beam affects mass balance due to space charge.
Nebulization Desolvation Vaporization, Atomization, Ionization
cones
The Sample Matrix – typical seawater
Element Atomic Weight 1st Ionization
Potential
Concentration
(mg/L)
Sodium (Na) 22.9898 5.138 10,800
Chlorine (Cl) 35.453 13.01 19,400
Magnesuim (Mg) 24.312 7.644 1,290
Sulfur(S) 32.064 10.357 904
Potassium (K) 39.102 4.339 392
Calcium (Ca) 40.08 6.111 411
Bromine (Br) 79.909 11.84 67.3
Agilent and ICP-MS
August 2007
Causes Ionization suppression
Forms polyatomic interferences
False response due to polyatomic molecules are greater
with heavier matrix.
Seawater
Agilent and ICP-MS
August 2007
0
20
40
60
80
100
120
140
Cal Blank
Cal Blank
0..25 /
25
5 / 500
100 / 10000
Blank
1000 ppm
Na C
heck
ICSAB
SeaWate
r 10:1
SeaWate
r 10:1
SeaWate
r 10:1
SeaWate
r 10:1
SeaWate
r 10:1
CCBCCB
SeaWate
r 10:1
+ 1
ppb
SeaWate
r 10:1
+ 1
ppb
SeaWate
r 10:1
+ 1
ppb
SeaWate
r 10:1
+ 1
ppb
SeaWate
r 10:1
+ 1
ppbCCV
SeaWate
r 10:1
SeaWate
r 10:1
SeaWate
r 10:1
SeaWate
r 10:1
SeaWate
r 10:1
CCBCCB
SeaWate
r 10:1
+ 1
ppb
SeaWate
r 10:1
+ 1
ppb
SeaWate
r 10:1
+ 1
ppb
SeaWate
r 10:1
+ 1
ppb
SeaWate
r 10:1
+ 1
ppbCCV
SeaWate
r 10:1
SeaWate
r 10:1
SeaWate
r 10:1
SeaWate
r 10:1
SeaWate
r 10:1
CCBCCB
SeaWate
r 10:1
+ 1
ppb
SeaWate
r 10:1
+ 1
ppb
SeaWate
r 10:1
+ 1
ppb
SeaWate
r 10:1
+ 1
ppb
SeaWate
r 10:1
+ 1
ppbCCV
SeaWate
r 10:1
SeaWate
r 10:1
SeaWate
r 10:1
SeaWate
r 10:1
SeaWate
r 10:1
CCBCCB
SeaWate
r 10:1
+ 1
ppb
SeaWate
r 10:1
+ 1
ppb
SeaWate
r 10:1
+ 1
ppb
SeaWate
r 10:1
+ 1
ppb
SeaWate
r 10:1
+ 1
ppbCCV
CCBCCB
Li / 6 [#3]
Sc / 45 [#1]
Sc / 45 [#2]
Sc / 45 [#3]
Ge / 72 [#1]
Ge / 72 [#2]
Ge / 72 [#3]
In / 115 [#3]
Tb / 159 [#3]
Bi / 209 [#3]
1/10 Seawater replicates (n=10)
Initial calibration
CCVs and CCBs
Approximately 10% upward drift in sensitivity over 14 hours of continuous analysis of 1/10 seawater
The suppression and drift
is caused by the amount
of sample matrix –
dilution puts less sample
matrix into the ICP-MS,
giving tolerance
Undiluted
Seawater
Many challenges- How can these be
addressed?
Robustness > Design the sample introduction such that the sample
change doesn’t have such an impact
High solids nebuliser, low flow sample introduction system, wide torch
injector diammeter, High RF power, long residence time in the plasma.
Use a collision cell capable of dealing with the polatomic molecules
Helium collision for single quad or QqQ reaction
Dilution > Reduce the matrix back to the ideal (< 0.2% tds)
Challenges of Measuring High TDS samples
July 8, 2014
Confidentiality Label
7
Dilution
Offline
• LOR is increased by dilution factor
Online
• Solution based dilution online has a few limitations
• Slow
• Varies with varying matrix, if using peripumps the dilution ratio changes
over time
Aerosol dilution
The nebuliser aerosol is reduced but the total gas flow to
the plasma is maintained - aerosol is diluted into argon
High Matrix Introduction system
Aerosol dilution
Normal sample uptake rate ~0.4 mL min-1
Sample aerosol is diluted by addition of gas after the spray chamber
August 2007
Agilent and ICP-MS
Makeup (Dilution) gas in
to torch
to drain
Carrier gas in
Carrier gas – 0.23 L min-1
Makeup gas – 0.72 L min-1
Total gas flow = 0.95 L min-1
Combining aerosol suppression and ion diffusion -highly robust conditions -excellent stability for undiluted seawater
long-term stability for undiluted seawater (50ppb/5ppm spiked)
(repeated measurements of seawater for 15 hours)
0.5
0.7
0.9
1.1
1.3
1.5
0 50 100 150
measurement #
raw
co
un
ts (
no
rmali
zed
)
9 Be (He) 25Mg (He) 27Al (He)
39K (He) 43Ca (H2) 44Ca (H2)
51V (He) 52Cr (He) 55Mn (H2)
56Fe (H2) 58Ni (He) 59Co (He)
60Ni (He) 63Cu (He) 65Cu (He)
66Zn (He) 75As (He) 78Se(H2)
88Sr (He) 88Sr (H2) 95Mo (He)
107Ag (He) 111Cd (He) 114Cd (114)
121Sb (He) 137Ba (He) 208Pb (He)
232Th (He) 238U (He)
August 2007
Agilent and ICP-MS
New revision HMI = uHMI (Ultra HMI) • Increased dilution range to x100 – even higher
matrix capability
• Less matrix loading to interface, so better long-term
stability
• uHMI maintains high carrier gas flow through spray
chamber, so faster gas replacement and washout
Carrier gas flow
(L/min)
Total
gas flow
7700
HMI
7900
UHMI
HMI-4
(HMI-L)
0.6 0.8 0.95
HMI-8
(HMI-M)
0.35 0.68 0.95
HMI-25
(HMI-H)
0.23 0.5 0.95
HMI-50 N.A. 0.4 0.95
HMI-100 N.A. 0.33 0.95
UHMI
Dilution
Port
Other sample introduction considerations
Agilent Ar gas humidifier
• Assists when measuring high salt
solutions
• Uses a hollow fiber membrane tubing
to “wet” the aerosol
• Helps to reduce salt build-up in the
interface and at the nebuliser tip.
• 2 channels in one body for Carrier gas
and Dilution gas
Brine Analysis: Chemicals and Samples
Actual samples of nearly saturated salt water are not easy to
obtain.
In this experiment, artificial salt water was prepared from
commercial table salts. 30g of pure sodium chloride (Kanto
Chemicals, Japan) dissolved in 100g of UPW was used for
preliminary experiment (23%).
Calibration standards were prepared by spiking to this solution.
Samples for analysis were purchased in Japan and USA
Brine Analysis: Results and Discussion
The recovery rates were calculated by spiking to the actual salt
water with various concentration. Very good recoveries could
be obtained over a wide (20-250 ppb) concentration range.
Fig 2: Spiked concentrations Fig. 3. Recovery rates
Detection limits
• Detection limits were calculated from 3
standard deviations of calibration
blank counts from the mean. (3 sigma
DL)
• Internal standard was added online so
the counts are normalised to internal
standard signal.
7Li 0.064 65Cu 0.02 111Cd 0.015 26Mg 0.22 66Zn 0.033 118Sn 0.014
27Al 0.056 69Ga 0.003 121Sb 0.0052 34S 1020 75As 0.019 125Te 0.053 39K 1.9 78Se 0.034 127I 0.054
44Ca 0.73 79Br 5.6 133Cs 0.0017
48Ti 0.019 85Rb 0.012 138Ba 0.0016
51V 0.0065 88Sr 0.013 182W 0.0031
52Cr 0.027 90Zr 0.0048 197Au 0.0066
55Mn 0.013 95Mo 0.0043 202Hg 0.023
56Fe 0.064 107Ag 0.097 208Pb 0.0026
Table 3. Detection Limits in ppb (ug/L)
Long term stability test
• The long term stability of analyte concentration was examined by using
one of the salt sample solutions
• The stability graphs show that ISTD works very well.
• There was no need to clean the lenses after analysis
60%
70%
80%
90%
100%
110%
120%
130%
140%
0:00:00 1:00:00 2:00:00 3:00:00 4:00:00 5:00:01
No
rmal
ize
d c
on
cen
trat
ion
of
anal
yte
Elapsed time
7Li/6Li Nogas 26Mg/45Sc H239K/45Sc H2 44Ca/45Sc H248Ti/45Sc HEHe 55Mn/45Sc H265Cu/45Sc He 79Br/115In H279Br/115In HEHe 85Rb/103Rh He88Sr/103Rh HEHe 133Cs/159Tb Nogas138Ba/159Tb HEHe 208Pb/209Bi He
Fig. 4: 5 hours stability
Analysis of various type of table salts
• Salt samples #1-15: Sea or Rock salt from Japan, Mexico, Germany, South Africa, USA,
Pakistan, Mongolia
• Covers concentration range from <0.01 ppb to >1,000 ppm in Brine.
Mg Ca K
Ga Cs W
Zr
S
Excellent detection capability with He collision
Spectral interference from the major component (Cl) of salt
water was almost completely eliminated by He mode.
51V (ClO interference) and 75As (ArCl interference) were
detected at low concentrations in 23% NaCl.
V
BEC: 0.06 ppb
As
BEC: 0.2 ppb
Other productivity tools for the 7900 Integrated Sample Introduction System (ISIS 3)
• Increase the sample thru-put, and
save on Ar costs
• Close-coupled valve – very short
tube length so minimal
stabilization/rinse delay
• Easier tubing setup by color coding
• Piston pump for faster sample
uptake
• 3-way valve to switch between on-
line ISTD or tune solution
ISIS is compatible with Startup auto-
optimization functions and full
autotune
7 port valve
(incl. online
ISTD port)
Piston
pump
3-way
valve
January 2014
NPT SAPK, Agilent Restricted
21
Summary
7900 ICP-MS with UHMI makes it possible to analyze even
saturated salt water.
• Good stability
• Low detection limit
• Wide measurement range from ppt to >1,000 ppm
• Expands ICP-MS into fields where only AAS, ICP-OES or XRF have
previously been available.
• Low sample preparation