Achieving rapid analysis of Li isotopes in high-matrix and low-Li samples with MC-ICP-MS: new developments in sample preparation and mass bias behavior of Li in ICPMS

Abstract

The efficiency of accurate determination of the lithium (Li) isotopic ratio by MC-ICP-MS is limited by current chemical purification procedures and instrument settings. The elution curve drifts significantly for matrices with a high matrix (e.g., Ca), and must therefore be checked frequently. The mass bias behavior of Li in inductively coupled plasma mass spectrometry (ICPMS) is unclear, which restricts the analysis of Li isotope compositions at low signal intensities. A novel method to purify Li and analyze the Li isotopic ratio is robust for a large variety of samples, where the efficient capacity of the resin is improved. The time required for purification and the volume of acid are significantly decreased, and cation-exchange resins can be easily and rapidly cleaned for re-use. Shift of the Li elution peaks is diminished. The mass bias behavior of Li isotopes in the ICP is revealed through high-resolution imaging of Li intensity and isotopic ratio, and the most stable zone is identified. The method has been validated by analysis of standard geological reference materials over 1.5 years. We report the Li isotope composition of a dolomite standard GSR-12 (δ⁷Li = 13.55 ± 0.37‰, 2σ). The long-term external precision of this method is better than ±0.47‰ (2σ) for δ⁷Li, and is suitable for analysis of geological samples. The new method is faster, but also precise and accurate.