www.chemicalfingerprinting.laurentian.ca balz s. kamber laurentian university ultra-high purity...
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www.chemicalfingerprinting.laurentian.ca
BALZ S. KAMBER
Laurentian University
Ultra-high purity ICP-MS
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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: 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 $
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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
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Solution ICP-MS
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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)
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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