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Re-certification of the absolute isotopic composition of the natural lithium isotopic reference material (IRM), IRMM-016, requires measurements calibrated by means of synthetic mixtures of highly enriched lithium isotopes. Ten such mixtures were prepared by weighing and mixing of two well characterized, isotopically enriched, Li(2)CO(3) compounds. The starting materials, 99.981% enriched (6)Li, and 99.9937% enriched (7)Li, were purified by ion exchange, and the purified materials converted from LiOH to Li(2)CO(3) by reaction with CO(2). Ten new mixtures were prepared by mixing different weighted amounts of these dissolved Li(2)CO(3) carrier compounds. The compounds had an estimated level of impurities of 100 +/- 100 µg g{-1} (expanded uncertainty with a coverage factor of 2). In the ten mixtures, the n((6)Li)/n((7)Li) ratio varies from 0.025 to 14 and the achieved expanded relative uncertainty on the amount ratio prepared is typically 2E{-4}. These mixtures were then used to determine the correction factor, K, for mass discrimination of the measurement procedure and instrument concerned.

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Authors: QI H P ET AL, JRC Geel (BE)
Bibliographic Reference: Article: International Journal of Mass Spectrometry and Ion Processes
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