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: 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 $

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

Solution ICP-MS

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 ( g) 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% HNO 3, 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% HNO 3 Take 0.24 g aliquot, add internal standard for drift correction, dilute to 6 g with H 2 O 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% HNO 3 Attacked in ultra-clean Teflon vials with 0.25 mL HNO 3 conc. and 0.5 mL HF conc. 160degC Conversion with HNO 3 to boil off Si as SiF 4 and taken up in a few g of 5% HNO 3 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

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 234 U and 229 Th 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 HNO 3 and analyze in 2 mL of 5% HNO 3 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 % 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 234 U and 229 Th

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