Sample Introduction Systems

SOLID – LASER ABLATION -II

LA-ICP-MS Data Reduction Software

• Termite 2.0– R script for trace element determinations– https://www.blogs.uni-mainz.de/fb09-geosciences/termite/– Open source software R is required to use TERMITE– TERMITE is particularly useful for samples that are

homogeneous with respect to their major element composition (in particular for the element used as an internal standard) and when many measurements are performed using the same analytical parameters.

– Mischel, S. A., Mertz-Kraus, R., Jochum, K. P., and Scholz, D., 2017. TERMITE - An R script for fast reduction of LA-ICPMS data and its application to trace element measurements. Rapid Communications in Mass Spectrometry 31, 1079-1087.

LA-ICP-MS Data Reduction Software• LADR

– LADR is a stand-alone program, developed in .NET for Windows 7, 8, and 10, that is also compatible with Linux and macOS under Mono (full support to be announced by mid-2020). The software is able to load data files from all makes and models of ICP–MS instruments, and is compatible with all laser ablation platforms.

– identify and remove transient spikes;– correct for interferences;– model variations in gas blank intensity;– synchronize analysis intervals with laser firing time;– model and correct for down hole fractionation;– model calibration drift;– use secondary standards to correct for matrix effects;– add unmeasured elements by stoichiometry;– quantify to an analytical total;– support mixed quantification routines within a data set;

– robust error propagation from all sources of uncertainty. – https://norsci.com/?p=ladr

LA-ICP-MS Data Reduction Software

• Iolite– Data reduction software package for both

trace element abundance determinations and isotope ratio calculations

– Version 3._ is installed on computer in MC-ICP-MS lab; used primarily for U-Pb dating applications

– Version 4.0 was introduced last year, very $$$, and thus version 3.0 is no longer supported

– https://iolite-software.com/

LA-ICP-MS Data Reduction Software

• ICPMSDataCal– Developed by Yongsheng Liu, China University of Geosciences, Wuhan– Written in the Visual Basic programming language and works on the

Microsoft Excel– It integrates the calibration and correction methods for trace element

analysis of silicate mineral, carbonate, metal oxide, sulfide minerals and single melt/fluid inclusion by LA-ICP-MS

– Isotopic ratios of Li, Sr, Nd, Hf, Os and Pb measured by LA-MC-ICP-MS– Data reduction of zircon U-Pb dating and trace element analysis can be

quickly conducted simultaneously– Time-dependent sensitivity drift can be corrected by the measurement

of quality control reference materials, which can be easily chosen by user;

– External standards can be automatically identified and easily changed (replace, add and delete) by the user;

LA-ICP-MS Data Reduction Software

• Glitter– developed by the ARC National Key Centre for Geochemical Evolution

and Metallogeny of Continents (GEMOC) and CSIRO Exploration and Mining, Australia

– GLITTER is written in the IDL programming language and provides cross-platform support for a number of environments, including Windows, MacOS, and Unix.

– First commercially available LA-ICP-MS Data Reduction Software package (developed and marketed in late 1990s – early 2000s)

– http://www.glitter-gemoc.com/

GLITTER

• On-line, interactive data reduction software package for laser ablation-ICP-MS instrumentation

• GLITTER - GEMOC Laser ICPMS Total Trace Element Reduction software package

GLITTER• GLITTER consists of five main interactive user interfaces

("windows"):

• The GLITTER "Main Window", containing the main menu options and the table of results.

• The "Standards" window, calling for the user to input the identity and values of the internal standard.

• The "Review" window, where the time-resolved laser signals are viewed and integration intervals are selected by the user.

• The "Plot" window(s), where data are visualised in various ways.

• The "Options" window, where the user can control the yield interpolation options, background fitting, magnitude of uncertainty estimates etc.

GLITTER – Main Page

Can be used to display various results, e.g., cps, concentrations, detection limits

GLITTER – Standards Page

- Identify the internal standard and enter the values in the table provided.- Internal standards can be changed at any time during the session.- Up to three isotopes can be used as internal standards, and are chosen from drop lists.

GLITTER – Review Page

Selection of background and laser ablation ion signal intervals.

GLITTER – Plots Page- Displays various types of plots –

mainly used for data quality verification purposes

- Chondrite-normalized plots, with a choice of trace-element order

- X-Y scatter plots

- Histograms

- Run quality control data (drift, ablation rates, detection limits, backgrounds etc.)

- Concordia plots (for U-Pb dating)

GLITTER – Options Page- The type of yield interpolation to

apply across the standard analyses

- Control over the background fitting procedures

- Enabling or disabling the 60s timed-save feature

- The magnitude of the relative uncertainty associated with the internal standard values and standard reference material values

- A fractionation test (useful to measure the relative fractionation between 2 isotopes of the same element, such as 24Mg and 25M

Laser ablation analyses

• Calibration – choice of an appropriate external standard

– Ideally you would use a solid sample that is well characterized and homogeneous and has the same (matrix) properties as your sample –i.e. ‘matrix-matched’ (Sylvester, 2008)

– At times, this can prove somewhat difficult….

Laser ablation analyses• Internal Standardization

– in general, the signal from the laser is dependent upon the amount of material ablated

– However, the amount of material ablated van vary due to:

– variations in laser-sample coupling (how effectively laser ablates sample),

– variations in laser power,– variations in transport efficiency

Laser ablation analyses• Internal Standardization

– Typically, use an element contained in your standard material (‘external standard’) that has been accurately determined by another in-situ, high resolution method of analysis (e.g. electron microprobe) – this is then referred to as the ‘internal standard’(IS)

– In minerals, we often use CaO (wt%) or SiO2 (wt%) obtained from electron microprobe analysis (but can use any other element) as long as it is well characterized and doesn’t overlap with major ICP-MS spectral interferences

– This calibration process allows for any variations in ablation, transport, and laser power to be accounted for

Laser ablation analyses• Theory behind trace element abundance calculations:

• concni = (cpsnij /abundancej) / (yieldni)

• where:

• concni = the concentration of element i in analysis n • cpsnij = the mean count rate (background-subtracted) of

isotope j of i in analysis n • abundancej = natural abundance of isotope j • yieldni = cps per ppm of element i in analysis n

Laser ablation analyses• The yield of element i in analysis n is determined by:

• yieldni = yieldns * Int(yieldni / yieldns)std

• where:

• yieldns = cps per ppm of the internal standard s in analysis n

• Int(yieldni / yieldns)std = the ratio of the yield of element i in analysis n to the yield of the internal standard s in analysis n, interpolated over the standard analyses.

Laser ablation• STANDARDS – element abundance determinations

– For silicate minerals, typically use NIST (National Institute Standard Technology; http://www.nist.gov/index.html) fused glass beads (Standard Reference Material – SRM)

– SRM NIST 610 – elements present @ ~500 ppm– SRM NIST 612 – elements present @ ~50 ppm– SRM NIST 614 – elements present @ ~2 ppm

Laser ablation

• STANDARDS - element abundance determinations

– APATITE – Durango (e.g. Trotter & Eggins, 2006, Chem. Geol.; Simonetti et al., 2008, Archaeometry);

– GARNET – PN2 (Canil et al., 2003, CJES)

– ZIRCON – 91500, Mudtank, BR266, GJ-1 (Wiedenbeck et al., 1995; Geostand. Newsletter; Hoskin & Schaltegger, 2003, Mineral. Society Reviews; Jackson et al., 2004)

Laser ablation• STANDARDS – isotopic analysis

– Common Pb:• SRM NIST 610, 612, Broken Hill Amazonite Feldspar

– U-Pb dating:• ZIRCON – 91500, BR266, Mudtank, Temora, Plešovice, GJ-

1• TITANITE – Khan• APATITE – Madagascar, Emerald Lake, and Kovdor

- Hf isotope measurement:- ZIRCON – BR266, Plešovice

Laser ablation – STANDARDS

• The GLITTER software is loaded with several commonly used standard reference materials, e.g. SRM NIST glasses

• However, new external standards can be uploaded within the software

Laser ablation• Laser ablation sample cell should house

the unknown sample and standard material simultaneously

• Typically, a sequence of laser ablation analyses of unknowns are bracketed (before and after) by analyses of standard material – referred to as ‘Standard-Sample Bracketing’ technique

Laser ablation

• Time-resolved spectra (time vs. ion signal intensity – cps)

• Analysis includes an interval prior to the start of the laser ablation process for measurement of the ‘background’ or ‘baseline’ (cps) – usually in the order of 45 to 60 seconds

Laser ablation• Background measurement is followed by

ablation of sample for a duration of ~60 seconds or less for most applications

• The duration of the ablation experiment is a function of:

– Abundances of elements under investigation– Coupling efficiency of material being ablated– Thickness of your sample section

Laser ablation

• In GLITTER, time-resolved spectra is accessed via the ‘Review Signal Selection’ option’

– In this window, you select your background, sample ion signal plateau, and the isotope to monitor

Laser ablation – GLITTER

Laser ablation• Lack a well characterized standard?

– One option is to report elemental ratios and not absolute abundances

– However, when doing so, user is assuming that elemental ionization is identical for all elements during the ablation process (in cell), transport and within the plasma itself

– This assumption holds true or is within the typical analytical uncertainty associated with laser ablation analyses (i.e. 5 to 10%) when……

Mass difference between elements being investigated is kept to aminimum!

Laser ablation – sampling strategy?

• Single spot vs. Rastering?– LIEF (laser induced elemental fractionation) is a

progressive change in the ratios of measured signals of certain element pairs with the increasing number of laser pulses applied to the sample

• LIEF may occur at:– Ablation site (result of evaporation/condensation

processes)– During transport to the plasma– In the plasma itself (incomplete volatilization of

particles)

Laser ablation• Previous studies have indicated that complete

atomization and ionization of laser ablated particles is subject to their size and composition, and temperature (plasma) and particle trajectory

• Overall, LIEF consists of two components:– constant bias resulting from ‘non-stoichiometric’

ablation;– time-dependent fractionation that results in a change

in the particle composition, number and size during the laser ablation process

Laser ablation – particle size distribution

• Several previous studies have shown that the size distribution of particles produced during laser ablation exert a significant control on the nature and size of elemental and isotopic fractionation

• Major factors affecting the size distribution of particles making their way to the ICP source are:

– the fluence– wavelength– pulse duration of the laser– the aspect ratio of pit– composition of the sample carrier gas– the size-dependent transport efficiency of the ablated particles.

Laser ablation

• It has also been shown that particle size distribution changes during a single analysis subject to the parameters listed above but it also depends on absorption of laser radiation by the sample (Horn et al. 2001) and the sampling strategy, i.e. scanning (raster) or stationary (single spot) ablation.

Laser ablation – sampling strategy

Sampling strategies using different types of laser. SEM images of static (left image) and scanning (right image) ablation craters in NiS produced with a non-homogenized 266 nm Nd:YAG laser (Kosler, 2008)

Laser ablation – sampling strategy

Optical microscope images of laser craters produced by static ablation (side view, crater diameters are 30 and 60 μm) and box raster laser scanning in zircon ablated by a non-homogenized 266 nm Nd:YAG laser (modified from Košler & Sylvester 2003),

Laser ablation – sampling strategy

SEM images of box raster and single laser pits produced by a non-homogenized 196 nm femtosecond laser in zircon (left image) and a corresponding detail of the bottom of the laser crater (right image).

Laser ablation – sampling strategy

• The major difference between stationary vs. rastering sampling modes is a rapid decrease in particle size and signal intensity for ablation with stationary beam compared to more steady signal and less change in particle size distribution while the laser beam scans across the sample surface.

Temporal variations of mass concentrations of particles determined by a TSI DustTrak 8520 laser photometer which has a capability to detect particles >0.3 μm (data from Košler et al. 2005a). The aerosol was generated by ablating silicate NIST-612 glass in He atmosphere with a 266 nm Nd:YAG laser fired at 10 Hz repetition rate.

Laser ablation – sampling strategy

Almandine

Pyrope

Scanning Static

Laser ablation – sampling strategy• Stationary vs. Scanning (rastering) of almandine and

pyrope garnet:

– The laser ablation conditions were similar to those used for trace element analysis in silicate minerals

– The laser was a 213 nm Nd:YAG, 10 Hz repetition rate and 3 J/cm2 for 90 seconds (total of 900 pulses)

– Produced round laser pits that were 25 and 40 μm in diameter in the garnets

– 150x25 and 150x40 μm trenches were produced by using identical ablation conditions while moving the stage under stationary laser beam at a speed of 10 μm/s.

– Volume of ablated material calculated from dimensions of craters– The results suggest that the volume of ablated material while

using laser scanning mode is ca 15% larger compared to the volume of material removed during stationary ablation, irrespective of laser beam diameter and color of the garnet.

Laser ablation – sampling strategy

• However,– The total number of counts obtained from laser

scanning during ablation of different sample matrices and for different lasers and ablation conditions is 20 –100% larger compared to signal intensities obtained from stationary ablation sampling

– The ablation time required for achieving comparable precisions by the two sampling strategies is at least 20% shorter for laser scanning and accordingly, the spatial resolution of laser scanning ablation is similar, or better, compared to the stationary ablation.

Laser ablation – sampling strategy & imaging prerequisite

SEM photo of ablated zircon Cathodoluminescence photograph of same zircon grain

Laser ablation - summary• Laser ablation is an excellent tool for semiquantitative to

quantitative analysis of many geological/solid samples

• Realistically, you should expect anywhere between 5 to 10% RSD (relative standard deviation @ 2 sigma level) for precision on elemental abundance determinations

• Benefits of spatial resolution outweigh any drawbacks

• Choice of appropriate, matrix-matched ‘external standard’ material, optimization of instrument parameters (both laser and ICP-MS instrument), and selection of sampling strategy are critical parameters for accuracy and precision

Laser ablation data – GLITTER• Elemental abundances are reported in an excel

compatible .csv file

One Sigma Error - The one sigma error estimates use √N counting statistics on the signal and background counts, propagated through the equations. An assumed 1% uncertainty (relative) on the elemental concentrations of the reference material, and a 3% uncertainty (relative) on the values of the internal standard is propagated throughout the calculations. These values can be changed, or turned off completely by the user via the “Options” window.

Laser ablation data - GLITTERThe Minimum Detection Limit

- The detection limit (MDL) at the 99% confidence level is determined by Poisson counting statistics:

• MDL = 2.3* √(2B) • where B is the total counts in the

background interval.