Purification of High Aluminum Content Samples for Rapid and Precise Analysis of Lithium Isotopes

Abstract

The analysis of lithium isotopes in high-aluminum content samples was accompanied by significant tailing of Al on Li using the traditional single-column method regardless of using single HCl or HNO3 as eluent. This hindered the precise determination of Li isotopes and made one-step column chromatographic separation of Li in silicate rocks challenging. Additional column procedures may be required to separate Li from Al in high Al samples, which would be time-consuming and result in reagent waste. In this study, the use of a 10 mL 0.2 mol L -1 HF and 0.5 mol L -1 HCl mixed eluent significantly reduced the Al tailing to less than 1% of that observed with the traditional method. The proposed purification procedure is applicable to a wide range of geological samples or minerals (e.g., silicates, seawater, sediments, and feldspars). Additionally, the matrix effect of Al and the Li concentration effect were investigated for accurate Li isotope analysis. The concentration effect, which was proved mainly led by the inappropriate treatment of the baseline. The real concentration effect yielded only a bias of 0.2‰ if normalized the solution of 20 ng g -1 Li with that of 140 ng g -1 . In accounting for this, Li isotopes can now be analyzed quite accurately at variable concentrations during non-strictly concentration-matched conditions. The longterm external precision of δ 7 Li based on the international standard LSVEC was approximately ±0.2‰ (2SD), making it suitable for geological sample analyses. The proposed method was confirmed through the analysis of BCR-2, BHVO-2, AGV-2, BIR-1a, RGM-2, JF-1, SCo-1, GSP-2, GSR-6, and GSR-8. All the results agreed with previously published values. Besides, two in-house Li isotope solution standards CAGS-Li-P (6.25±0.25‰) and CAGS-Li-N (-15.02±0.18‰) were developed and routinely analyzed to monitor the instrumental mass bias.