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www.chemicalfingerprinting.laurentian.ca

Ultra-high purity ICP-MS. BALZ S. KAMBER Laurentian University. www.chemicalfingerprinting.laurentian.ca. Drivers behind geo- and cosmochemical analysis. Desire to analyze sub-nanogram quantities of implanted solar wind, returned cometary material, dust in Antarctic ice, etc.

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www.chemicalfingerprinting.laurentian.ca

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  1. Ultra-high purity ICP-MS BALZ S. KAMBER Laurentian University www.chemicalfingerprinting.laurentian.ca

  2. Drivers behind geo- and cosmochemical analysis Desire to analyze sub-nanogram quantities of implanted solar wind, returned cometary material, dust in Antarctic ice, etc.

  3. Analytic equipment: SIMS Secondary 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 $

  4. Analytic equipment: ICP-MS Inductively 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

  5. Solution ICP-MS

  6. Instrumental limits: ICP-MS Sensitivity: 450,000 cps ppb-1 Detection limit: 1 cps Consumed mass: 2 grams Absolute 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)

  7. 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

  8. Simple metal results

  9. Note outlier

  10. 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

  11. 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

  12. Chip results 10 mg samples Chip results sub 10 mg samples

  13. Chip results semi-quantitative mass scan

  14. Chip results semi-quantitative mass scan

  15. 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

  16. 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)

  17. 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

  18. 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

  19. UV- laser idea

  20. 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

  21. 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

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