Lithium isotope analysis on the Neoma MS/MS MC-ICP-MS

Abstract

Lithium isotopes are measured routinely using multi-collector inductively coupled plasma mass spectrometry due to the high throughput and high measurement precision capabilities of this technique. To obtain high precision isotopic data, lithium is generally purified through ion exchange resins to reduce compositional matrix effects and minimize isobaric interferences when analyzed in solution. In this work, we demonstrate that the ThermoScientific Neoma MS/MS MC-ICP-MS can be used to measure high precision lithium isotopic ratios after purification for a variety of geological and environmental matrices. While the double-Wien filter of the Neoma MS/MS requires additional considerations for measuring lithium isotopes compared to previous generation instruments, high precision lithium isotope ratios can be achieved with proper tuning of the lenses. We provide a strategy for optimization of ⁶Li/⁷Li measurements for precision and measurement stability, and show our long-term reproducibility for NIST924a and IRMM-016 was 0.8‰ and 0.5‰, respectively. In addition, we provide new ⁶Li/⁷Li measurements for several environmental reference materials without Li isotope data in the literature, including NIST SRMs 1646a, 2706, 2711a, 2780a, and 4350b.