www.chemicalfingerprinting.laurentian.ca

BALZ S. KAMBER

Laurentian University

Ultra-high purity ICP-MS

Drivers behind geo- and cosmochemical analysis

Desire to analyze sub-nanogram quantities of implanted solar wind, returned cometary material, dust in Antarctic ice, etc.

Analytic equipment: SIMSSecondary ion mass spectrometer

Pros: Ideal for in situ analysis, quasi non-destructive, high spatial resolution, high mass resolution, for some elements ppt detection limits

Cons: sample in ultra-high vacuum, requires perfect surface for ppt analysis, matrix effects, slow, and $

Analytic equipment: ICP-MSInductively coupled plasma mass spectrometer

Pros: ppq detection limits, can work in situ or analyze digests, samples at atmospheric P, matrix insensitive, fast, relatively inexpensive

Cons: destructive, requires more material than SIMS, prone to blank contamination during sample preparation, may require elemental pre-concentration

Solution ICP-MS

Instrumental limits: ICP-MSSensitivity: 450,000 cps ppb-1

Detection limit: 1 cpsConsumed mass: 2 gramsAbsolute mass of detected material: 4-5 femtograms (10-15g)

Dilution factor (solution/solid ratio): 1,000

Hence in 2 g of solution, only 2 mg of solid translates to minimum detectable concentration of 4-5 nanograms g-1 (ppt)

Current standard practice for easy metal (e.g. Cu)

•Up to 0.25 g of sample dissolved

•Metal or alloy dissolves slowly in 10% HNO3,

in pre-cleaned 0.25 L PP bottle

•Take 2 g aliquot, add internal standard for drift

correction and run on ICP-MS

•Analysis includes a semi-quantitative mass

scan

Simple metal results

Note outlier

Current standard practice for pesky metal (e.g. certain bronzes)•Up to 0.25 g of sample dissolved •Alloy attacked by aqua regia in ultra-clean Teflon vials at 160degC, converted with HNO3 and taken up in 10g of 20% HNO3

•Take 0.24 g aliquot, add internal standard for drift correction, dilute to 6 g with H2O and run on ICP-MS

•Abandoned U & Th pre-concentration (blank)•Analysis includes a semi-quantitative scan

Current standard practice for Si-based, HFSE-doped chips

•Very small chips (a few mg) rinsed in ultra-clean 5% HNO3

•Attacked in ultra-clean Teflon vials with 0.25 mL HNO3 conc. and 0.5 mL HF conc. 160degC

•Conversion with HNO3 to boil off Si as SiF4

and taken up in a few g of 5% HNO3 with internal standards

•Run on ICP-MS, including a semi-quantitative scan

Chip results 10 mg samples

Chip results sub 10 mg samples

Chip results semi-quantitative mass scan

Chip results semi-quantitative mass scan

Ideas for new procedures

•Wipes

•Metals and chips: improve detection limits by

chromatographic matrix exclusion

•Pre-concentrated U and Th: improve blanks

and counting statistics by laser ablation

•Addition of 234U and 229Th spikes

Wipes

•Combust in quartz crucibles in SNO above-ground facility

•Take-up ash into 6mL Teflon vessel•Digest ash in 0.2mL HF•Convert with HNO3 and analyze in 2 mL of 5% HNO3 with internal standards

•Common procedure for environmental samples (peat)

Matrix removal

•Previous efforts at pre-concentrating Th and U focused on ion chromatography that specifically retains U and Th

•This is the method preferred by Patricia Grinberg

•For small samples, this method reaches a blank limit as the U-TEVA resin itself appears to contain a blank

•Alternative is to remove matrix (all 1+, 2+ and 3+ charged cations) on cation exchange resin

Analyze pre-concentrated U and Th as a UV-laser induced

aerosol

•Dry down U and Th pre-concentrate into

inert clean Teflon vial

•Vaporize residue (and Teflon) with a few

pulses of an Excimer laser

•Transport aerosol into ICP-torch in

99.9995% He clean stream

UV- laser idea

Analyze pre-concentrated U and Th as a UV-laser induced

aerosol

•Higher ionization efficiency, larger signal,

lower blank

•But need for yield monitor: isotope dilution

•Addition of known amount of isotopically

enriched 234U and 229Th

Outlook•Simple metals with low contamination risk and wipes can be handled with existing protocols in lab

•Dangerous metals (Pb, certain bronzes) and HFSE-doped chips need to be digested in a non-geochemical/cosmochemical lab

•We can train personnel to learn these techniques

•Publication quality experiments should be performed by a Postdoc