SIMULTANEOUS MEASUREMENT OF LITHIUM AND BORON ISOTOPES AS LITHIUM TETRABORATE ION BY THERMAL IONIZATION MASS-SPECTROMETRY

A method for the measurement of Li2BO2+ ions by thermal ionization mas s spectrometry employing a Daly ion-counting system was examined. By s olving simultaneous quadratic equations of intensity ratios ranging be tween m/z 55 and 57, and between m/z 56 and 57, precise and accurate m easurement of lithium and boron isotope ratios can be carried out simu ltaneously. The intensity ratio between m/z 54 and 57 can be used to c heck the internal consistency of the lithium and boron isotope ratios obtained. The isotopic fractionation rate with the species Li2BO2+ was low. Prior to measurement, a two-column ion exchange process was used to separate lithium from the sample matrix and then to convert LiCl i nto LiOH, which subsequently reacts with H3BO3 to form lithium tetrabo rate. Lithium and boron isotope ratios were successfully measured simu ltaneously with precisions (relative standard deviations) of 0.05% for lithium and 0.01% for boron.