PRECISE LITHIUM ISOTOPIC ANALYSIS BY THERMAL IONIZATION MASS-SPECTROMETRY USING LITHIUM PHOSPHATE AS AN ION-SOURCE MATERIAL

A high-precision Li isotope analysis was developed for determining the Li+ ion emitted from lithium phosphate as an ion source material by a Re double-filament ionization method in the thermal ionization mass spectrometry. In this method, Li isotopic fractionation is distinctly less sensitive to the filament temperature than those in the previous methods, and stable and high ion beam intensity of more than 8 x 10(-11) A for Li-7 is obtained. These advantages in determining the Li-7/Li-6 ratio result in the analytical reproducibility of 0.26 parts per thousand (1sigma). Furthermore, the sample preparation is simple and the low temperature (850-degrees-C) required by this method ensures the analysis of the isotopic composition of small amounts of Li with less influence of Li contamination to the sample, compared with the previous methods.