www.chemicalfingerprinting.laurentian.ca

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

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Simple metal results
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Note outlier
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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

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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

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Chip results 10 mg samples
Chip results sub 10 mg samples
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Chip results semi-quantitative mass scan
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Chip results semi-quantitative mass scan
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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

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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)

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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

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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

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UV- laser idea
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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

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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