Precise and accurate boron and lithium isotope determinations for small sample-size geological materials by MC-ICP-MS

Yung-Hsin Liu, Kuo-Fang Huang, Der-Chuen Lee

Index: 10.1039/C7JA00400A

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Abstract

A low-blank, high-precision and highly reproducible technique for boron (B) and lithium (Li) isotope analyses by Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS) were developed in this study. The new analytical protocol presented here involves effective sample dissolution, simultaneous purifications of B and Li, together with high-precision B and Li isotopic determinations on silicate matrices. The sample solutions prepared from the low-temperature acid-dissolution have nearly 100% yields for B, Li, and Be. B and Li can be extracted from the same aliquot through ion chromatographic separations, followed by a modified micro-sublimation technique for further B purification. The low procedural blanks of Li and B using this new analytical protocol enable us to process silicate samples with trace amounts of B (< 80 ng) and Li (< 1 ng). The long-term external precisions of δ11B (5 ng of B) and δ7Li (1 ng of Li) are better than ± 0.35‰ (2SD) and ± 0.27‰ (2SD), respectively, based on the measurements on a series of international reference materials over the last two years. The measured δ11B and δ7Li values for the rock standards with a variety of matrices, including JR-2, JA-1, AGV-2, JB-2, BCR-2, BHVO-2, and IAEA-B5, are in excellent agreement with the published values, demonstrating the robustness of our new analytical protocols. Applying this improved technique, we are able to generate accurate and high-precision δ11B and δ7Li data for B- and Li-depleted natural samples, such as meteorite materials and ultramafic rocks, which can provide critical constraints on early solar system geochemistry and mantle compositions.