A Simplified, Accurate and Fast Method for Lithium Isotope Analysis of Rocks and Fluids, and δ7Li Values of Seawater and Rock Reference Materials |
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| Authors: | Martin Rosner Lary Ball Bernhard Peucker-Ehrenbrink Jerzy Blusztajn Wolfgang Bach Jörg Erzinger |
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| Institution: | Inorganic and Isotope Geochemistry Section, GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany;Woods Hole Oceanographic Institution, Clark Laboratory, Woods Hole, MA 02543, USA;Petrology of the Ocean Crust, University of Bremen, Klagenfurter Straße, 28334 Bremen, Germany |
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| Abstract: | We report a new approach to conduct fast and accurate lithium isotope ratio measurements by MC-ICP mass spectrometry after wet chemical sample preparation. In contrast to most previously published methods our MC-ICP-MS set-up did not use a desolvating system to achieve appropriate ion beam intensities and, therefore, was less affected by matrix-induced shifts of the instrumental mass bias. As the total lithium background and build-up in the sample introduction system was low, previous sample residues could be washed out by an extended uptake of the new sample. Elimination of a nitric acid rinse step increased the sample throughput by a factor of two and allowed the instrumental mass bias drift to be tracked more precisely. δ7Li values of powdered silicate rock reference materials and seawater obtained in this study revealed good accuracy and an overall analytical uncertainty of typically 0.5‰ (2s). On the basis of a comparison between our lithium isotope data and compiled literature data, we recommend preliminary average δ7Li values for seawater (+30.8‰) and several silicate rock reference materials (BHVO-1: +5.0‰; JA-1: +5.6‰; JB-2: +4.8‰). The compilation of published δ7Li values for seawater suggests that the observed large lithium isotope differences are due to inter-method and/or interlaboratory bias. Most recently published δ7Li values for seawater show little variation and confirm a constant lithium isotope composition (at the sub ‰ level) of seawater in well mixed ocean basins. |
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| Keywords: | lithium isotopes MC-ICP-MS seawater silicate reference material matrix effect |
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