Rapid Purification of Alkali and Alkaline-earth Elements for Isotope Analysis (δ 7Li, δ 26Mg, 87Sr/86Sr, and δ 88Sr) of Rock Samples Using Borate Fusion Followed by Ion Chromatography with a Fraction Collector System.

Abstract

For the rapid, easy, and safe purification of alkali and alkaline-earth elements from rock samples for stable isotope analysis, we developed a semi-automated, high-throughput procedure using borate fusion and an ion chromatography system equipped with a fraction collector. This HF-free procedure for the decomposition of silicate rock samples can be performed in a short time without isotope fractionation; the purification procedure enables the collection of baseline-separated peaks of multiple target elements and the complete removal of interference matrices from reagents and samples. The accuracy of this procedure was verified by confirming the correspondence of stable isotopic values of Li, Mg, Sr (δ7Li, δ26Mg, δ88Sr) and radiogenic isotopic values of Sr (87Sr/86Sr) to previously reported values in various geochemical reference materials in which the concentration range of Li was 7.78 - 86.6 ng g-1, that of Mg was 0.02 - 26.9%, and that of Sr was 178 - 7240 ng g-1. These results demonstrate that this procedure, which allows for the concurrent multi-isotope analysis of alkali and alkaline-earth elements in the same sample, is applicable to a wide variety of sample types.