Accurate lithium isotopic analysis of twenty geological reference materials by multi-collector inductively coupled plasma mass spectrometry

The lithium (Li) isotopes can be used to track the evolution of continental silicate weathering, which has an important role in maintaining Earth's long-term climate stability. At present, complex separation procedures and analytical mass bias restrict the accurate determination of Li isotopic compositions in various geological samples with different Li concentrations and matrix/Li ratios. Here, an optimization of dual-column chromatography achieves high Li recovery, low procedural blank, and low Na/Li ratio (< 1) after purification, allowing the acquisition of high precision Li isotope ratios by a Nu Plasma 3 multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). In order to evaluate the accuracy of new method, the δ7Li values of BHVO-2, BCR-2, AGV-2, JG-2, RGM-2, SGR-1b, GSR-6, GSR-12, and seawater, are repeatedly analyzed more than 3 times each and are consistent with the published data within the uncertainty. The long-term external reproducibility of δ7Li based on L-SVEC and IRMM-016 pure solutions is about ±0.2‰ (2SD), and is suitable for analysis of geological samples. These results suggest that new dual-column method is reproducible and reliable. We also report ten new reference materials including two USGS rocks (SDC-1: 1.8 ± 0.4‰; W-2a: 2.9 ± 0.3‰), four soils (GSS-3: 1.3 ± 0.2‰; GSS-4: −5.1 ± 0.4‰; GSS-6: −1.9 ± 0.3‰; GSS-8: 0.4 ± 0.3‰), and four stream sediments (GSD-6: −1.0 ± 0.4‰; GSD-11: 1.1 ± 0.3‰; GSD-12: 1.8 ± 0.2‰; GSD-14: 1.6 ± 0.4‰), all previously analyzed for K isotopes. There is significantly fractionation of Li and K isotopes during silicate weathering. Compared to the K isotopes, Li isotopes have more promising as an isotope tool for weathering due to its larger fractionation and its abiotic property.