High precision measurements of lithium isotopic composition at sub-nanogram by MC-ICP-MS with membrane desolvation.

Abstract

The geochemistry of Li and Li isotopes is a promising tracer of chemical weathering processes for both modern and ancient times. Therefore, accurate and precise determination of the isotopic composition of Li is required for a large variety of complex geological samples with different Li concentrations and matrix/Li ratios. Especially, geochemical studies of precious geological samples with ultra-low lithium content and high matrix. In this study, the accuracy and the precision corresponding to Li isotopic measurements of low-level samples using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) with membrane desolvation introduction system was evaluated. The method of MC-ICP-MS with membrane desolvation and a high-sensitivity X-skimmer cone, together with a simple one-step column separation enabled the high-precision isotopic analysis of Li quantities as small as 2 ng. The long-term instrumental external reproducibility of δ7Li values for the L-SVEC and SPEX-Li were 0.0 ± 0.1‰ (n = 20) and 12.1 ± 0.4‰ (n = 20), respectively. Based on the measurements on a series of international reference materials over the last two years. The measured δ7Li values for the standards with a variety of matrices, including BHVO-2, AGV-2 and seawater (NASS-6). The δ7Li values of BHVO-2 (4.58 ± 0.35‰), AGV-2 (6.85 ± 0.40‰) and NASS-6 (30.88 ± 0.20‰) are in agreement with the published data within the uncertainty. We also present analytical results for South China Sea surface seawater water, meteorite, limestones and rain water. These results demonstrate the validity of the method for obtaining highly precise and accurate outcomes.