Optimisation of Lithium Chromatography for Isotopic Analysis in Geological Reference Materials by MC-ICP-MS

The lithium isotope system can be an important tracer for various geological processes, especially tracing continental weathering. The key to this application is the accurate and precise determination of lithium isotopic composition. However, some of the previously established column separation methods are not well behaved when applied to chemically diverse materials, due to the significant variations in matrix/lithium ratios in some materials. Here, we report a new dual-column system for lithium purification to achieve accurate and precise analysis of lithium isotopic compositions using a multi-collector inductively coupled plasma-mass spectrometer (MC-ICP-MS). Compared with single-column systems, our dual-column system yielded a consistent elution range of the lithium-bearing fraction (7-16ml) for samples with a large range of lithium loads and matrix compositions, so that column re-calibration is not required. In addition, this method achieved complete lithium recovery and low matrix interference (e.g., Na/Li1) with a short elution time (similar to 6h, excluding evaporation), with the entire procedure completed in 1.5days. We report high precision Li isotopic compositions in twelve chemically diverse materials including seawater, silicates, carbonates, manganese nodules and clays. New recommended Li isotopic values and associated uncertainties are presented as reference values for quality control and inter-laboratory calibration for future research and were consistent with previously published data. However, significant lithium isotopic variances (similar to 1 parts per thousand) in BHVO-2 from different batches suggest Li isotopic heterogeneity in this reference material and that Li isotopic studies using this reference material should be treated with caution.