High-yield lithium separation and the precise isotopic analysis for natural rock and aqueous samples

A high-yield lithium separation technique for rock and aqueous samples has been established together with precise Li isotope analysis by thermal ionization mass spectrometry. Four separate stages of ion-exchange chromatography were carried out using organic ion-exchange resin. An ethanol-HCl solution was used for complete separation of Li from Na at the third column stage. Total reagent volume for the entire chemical process was reduced to 42 ml and 33.3 ml for rock samples and seawater, respectively. The recovery yield and total procedural blank are 99.2-99.3% and 11 pg, respectively. Li₃PO₄ was used as an ion-source material in the mass spectrometric analysis. The in-run precision and reproducibility of measured ⁷Li/⁶Li ratios were ±0.04-0.07‰ (2σ_mean) and 0.37‰ (relative standard deviation; RSD) for rock and ±0.05-0.08‰ (2σ_mean) and 0.35‰ (RSD) for seawater. In this method, Rb, Sr, Sm, Nd, La and Ce can be collected after Li elution in the first column chromatography, then separated by the following specific procedures for these elements. Therefore, this method makes possible multi-isotope analysis for Li-poor and restricted small amounts of samples such as meteorites and mantle materials, extending to Li isotope geochemistry and cosmochemistry.