Extraction of lithium from GSJ rock reference samples and determination of their lithium isotopic compositions

Li was extracted completely from the Geological Survey of Japan (GSJ) rock reference samples by HF-HCl decomposition and separated from other alkali metal ions by cation exchange chromatography. The degree of Li isotope fractionation during the preparations of samples for mass spectrometry for Li isotopic ratio measurements was, therefore, negligible. The isotopic compositions of Li extracted from the GSJ samples were measured by double-filament surface ionization mass spectrometry. The permil (parts per thousand) deviation, delta(7)Li, of the Li-7-to-Li-6 ratio of one of the GSJ samples (JR-1) from that of the Li isotope standard, IRM-016, was +3.9 parts per thousand, with a 95% confidence limit of 0.7 parts per thousand. The delta(7)Li values of the 16 GSJ samples varied in the range -2.5 to +6.4 parts per thousand. These data are probably the first such data obtained for the GSJ rock samples. No clear dependence of the delta(7)Li value on the kind of rock was observed.