An Intercomparison Study of the Germanium Isotope Composition of Geological Reference Materials

Type Article
Date 2012-06
Language English
Author(s) Escoube Raphalle1, 2, Rouxel OlivierORCID1, 3, 4, Luais Beatrice5, Ponzevera Emmanuel4, Donard Olivier F. X.1
Affiliation(s) 1 : LCABIE, U. Pau et Pays de l’Adour, CNRS UMR 525, Hélioparc 64053 Pau, France
2 : UEB-UBO, European Institute for Marine Studies IUEM, 29280 Plouzané, France
3 : Woods Hole Oceanog Inst, Marine Chem & Geochem Dept, Woods Hole, MA 02543 USA.
4 : IFREMER, Ctr Brest, DRO GM, F-29280 Plouzane, France.
5 : Nancy Univ, CRPG CNRS UPR 2300, F-54501 Vandoeuvre Les Nancy, France.
Source Geostandards And Geoanalytical Research (1639-4488) (Wiley-blackwell), 2012-06 , Vol. 36 , N. 2 , P. 149-159
DOI 10.1111/j.1751-908X.2011.00135.x
WOS© Times Cited 29
Keyword(s) germanium, isotope, intercalibration, reference materials, germanium, isotope, intercalibration, materiaux de reference
Abstract Recent analytical developments in germanium stable isotope determination by multicollector ICP-MS have provided new perspectives for the use of Ge isotopes as geochemical tracers. Here, we report the germanium isotope composition of the NIST SRM 3120a elemental reference solution that has been calibrated relative to internal isotopic standard solutions used in the previous studies. We also intercalibrate several geological reference materials as well as geological and meteoritic samples using different techniques, including online hydride generation and a spray chamber for sample introduction to MC-ICP-MS, and different approaches for mass bias corrections such as samplecalibrator bracketing, external mass bias correction using Ga isotopes and double-spike normalisation. All methods yielded relatively similar precisions at around 0.1 parts per thousand (2s) for d74/70Ge values. Using igneous and mantle-derived rocks, the bulk silicate Earth (BSE) d74/70Ge value was re-evaluated to be 0.59 +/- 0.18 parts per thousand (2s) relative to NIST SRM 3120a. Several sulfide samples were also analysed and yielded very negative values, down to -4.3 parts per thousand, consistent with recent theoretical study of Ge isotope fractionation. The strong heavy isotope depletion in ore deposits also contrasts with the generally positive Ge isotope values found in many modern and ancient marine sediments.
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