An efficient Li dual-column system and high-precision Li isotope measurement of high matrix and low-Li samples by MC-ICP-MS

Abstract

Over the last decade, there has been a growing interest in using lithium (Li) isotopes in marine carbonates to trace chemical weathering and clay formation in the Earth's history. Yet it remains technically challenging to precisely and efficiently determine the Li isotope composition in carbonate samples due to the imperfect Li separation led by the matrix effect and the extremely low Li concentration in carbonates relative to the analytical threshold of sample size. For such high matrix and low-Li samples, here we present an efficient dual-column chromatography system for Li purification. The dual-column system has a large loading capacity, fixed Li elution range of merely 12 mL, complete Li recovery (>99.5%) and relatively efficient total elution time (7 hours). The procedural blank is 0.036 ± 0.002 ng accounting for sample dissolution and chemical purification, and the Na/Li mass ratio of the Li cut is below 0.5. High precision and accurate Li isotope measurement is performed efficiently with a small sample-sized protocol developed on a MC-ICP-MS (Neptune plus) connected with an APEX 2-IR desolvator. The whole procedure is validated by analyzing a series of certified reference materials. The long-term external precision of δ⁷Li determined based on L-SVEC and a high-purity Li solution is 0.6‰ (2SD) and 0.9‰ (2SD) for a minimum sample size of 7.5 ng.