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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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slide1

Ultra-high purity ICP-MS

BALZ S. KAMBER

Laurentian University

www.chemicalfingerprinting.laurentian.ca

slide2

Drivers behind geo- and cosmochemical analysis

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

slide3

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 $

slide4

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

slide6

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)

slide7

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
slide10

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
slide11

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
slide12

Chip results 10 mg samples

Chip results sub 10 mg samples

slide15

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
slide16

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)
slide17

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
slide18

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
slide20

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
slide21

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