Jason Day and Sally A. Gibson12th BNASSPlymouth, 12-14 July 2004

Contact: jday01@esc.cam.ac.uk

Department of Earth SciencesUniversity of CambridgeDowning StreetCambridgeCB2 3EQUNITED KINGDOM

LALA--ICPICP--MS for the accurate determination of trace MS for the accurate determination of trace

elements in silicate rocks containing refractory elements in silicate rocks containing refractory

mineral phasesmineral phases

Whole rock chemistry HREE - igneous studies

Elemental ratios (Nb/U and/or Ta/Hf) commonly used for magmatic studies

Hf isotopic studies by MC-ICP-MS magmatic signatures

Elemental Determinations in Geochemistry

Microanalysis

Sensitivity better than microprobe

Multi-element capability

Fast, minimal sample preparation

Ability to analyze small or difficult samples

Benefits of LA-ICP-MS

The big question

Does this technique give comparable data to HF digestion ICP-MS?

Is LA-ICP-MS a serious contender?

Ilmenite, Zircon, Chromite, Spinel, Magnetite etc.

Difficult to dissolve, even with microwave and bomb techniques

Low recoveries by solution ICP-MS for heavy rare earths, Ta, Nb, Hf, Zr

Flux methods badly contaminate the instrument (Li and especially B)

Refractory Phases

Hf isotopic measurements on Barberton komatiites: effect of incomplete dissolution and importance for primary and secondary magmatic signatures

Blichert-Toft et al. 2004, Chemical Geology, 261-275.

Lithium Metaborate Flux Method

Concentrations (ppm) determined in 91SB29 (kimberlite sample)by LA-ICP-MS compared to flux dissolution and ICP-MS analysis

Element % RSD (n=4) LOD (ppb) LA-ICP-MS Solution % Laser RecZr 5.3 7.0 414.785 417.447 99Ba 1.0 12.9 1809.395 1838.301 98La 7.3 1.4 419.980 434.724 97Ce 1.9

Silicate Rock Digestion

100 mg of dried rock powder in Savillex vials

1 ml HNO3 (69%) plus 4 ml HF (40%) QD or Aristar grade (or better)

120 C for 12 hours (minimum)

HF evaporated off and sample redissolved in 50% HNO3

Diluted to 50 ml (0.1-0.2% TDS) (4% HNO3) for storage

Further diluted 5-10x, spiked with IS for analysis

EVAPOCLEAN

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BHVO-2 averageBHVO-2 litAGV-2 averageAGV-2 litBIR-1 litBOB-1 litSTM-1 lit

Results Solution ICP-MS

Error Bars 10%

Incomplete dissolution

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G-2 (HF)G-2 flux

G-2 lit

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0.8

% RSD

167.91.2Hf

2130963.5Zr

% RecG-2 lit (ppm)G-2 (ppm)

Error Bars 10%

Nd:YAG 1064nm fundamental wavelength (frequency quintupled)

Automated XY stage sample chamber

Ring, coaxial, and transmitted light

Cross polarisers

Laser spot sizes 1 120 m

MKS mass flow controller system calibrated for helium (0-2 l min-1) for precise control of the ablation gas (not shown)

New Wave UP213

Elan DRC II - ICP-MS

Normal ICP-MS conditions

No reaction gas used for this study

Tuning (XY, neb, autolens, daily performance, etc.) with NIST 612

Laser mode - Indium 10,000 cps ppm-1(NIST 612) - Intensity RSD 2%

Gas backgrounds through sample cell (blanks) = zero counts

Image courtesy Perkin Elmer LAS Maryanne Thomsen

Condensation blanket - Ar vs. He atmosphere

60 laser pulses display clear differences in the degree of condensation deposited back onto sample surface.Eggins, et al, Appl. Surf. Sci., (1998), 127-129, 299

Helium less dense than argon (10x)

Higher ionisation energy

High thermal conductivity enhances rapid removal of thermal energy and inhibits condensation of smaller particles

Helium ablation gas

Laser Sample Preparation Method

Place rock powders in graphite crucibles (no flux!)

Dry at 900C for 5 min then ramp to 1350C for 10 min

Quench quickly in Milli-Q water Mount on microscope slide Use NIST 610, 612, etc for ICP-MS

calibration Normalize trace element intensities to

a known major element (Ca) Glitter method of calculating concentrations

Campbell, I.H., Constraints on continental growth models from Nb/U ratios in the 3.5Ga Barberton and other Archaean basalt-komatiite suites American Journal of Science, 2003 (303) 319-351

Laser Software

Image courtesy New Wave Research Damon Green

Signal plot assessment of

1. Sample homogeneity 2. Laser performance

All elements constant throughout analysis?

BCR-2 100 m

G-2100 m

Some elements NOT constant throughout analysis!

Zr, Hf spikes in data - Zircon

LA-ICP-MS for USGS SRMChondrite Normalised REE

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AGV-2g

AGV-2g

AGV-2g

AGV-2 lit

Chondrite values taken from Sun and McDonough, 1989 Magmatism in the Ocean Basins 313-345

Error bars 10%

Concentrations (ppm) determined in BCR-2 (basalt SRM)by LA-ICPMS compared to certified values

BIR-1, BHVO-2, AGV-2, and others give similar results

Calibration is 5-10% accurate for international standards

Element % RSD (n=4) LOD (ppb) LA-ICP-MS Certified % Laser RecZr 1.9 7.0 169.305 188 90Ba 1.1 12.9 689.075 677 102La 1.5 1.4 22.920 24.9 92Ce 2.5

Results

Concentrations (ppm) determined in BD1072 (kimberlite sample) by LA-ICPMS compared to aqueous solution analysis

Element % RSD (n=4) LOD (ppb) LA-ICP-MS Solution % Laser RecZr 0.2 3.8 276.935 238.594 116Ba 5.0 8.6 1254.705 1243.220 101La 3.1 1.3 142.005 148.965 95Ce 3.8 0.8 287.965 300.620 96Pr 8.2

Agreement with certified values for USGS rock standards

Precision for some samples comparable to liquid sample ICP-MS

Higher recoveries for certain elements in refractory mineral phases

To increase accuracy and precision, analyse a small number of isotopes and increase the number of replicates

Conclusions

Future Work

Sample heterogeneity (sampling uncertainty estimates) for bulk analysis

Elemental fractionation (isotope analysis)

Comparison to peroxide fusion methods?

Single mineral analysis

MC-ICP-MS

Acknowledgements

Maryanne Thomsen (Perkin Elmer, UK)

Detlef Gnther and Bodo Hattendorf(ETH, Zurich)

Damon Green and Grant Bennett (New Wave Research, UK)

University of Cambridge Department of Earth Sciences

Mike BickleHarry ElderfieldAlbert Galy

Thanks for your attention!