Isotope dilution thermal ionization mass spectrometry for determination of concentration of enriched lithium using NaLiBO.sub.2.sup.+ ions

Calibration of .sup.6Li enriched spike by Reverse IDMS was carried out by monitoring molecular ion species NaLiBO.sub.2.sup.+ at m/z 71, 72 and 73 together with Na.sub.2BO.sub.2.sup.+ at m/z 88 and 89. Two independent .sup.6Li/.sup.7Li ratios were obtained from two ion intensity ratios, .sup.73I/.sup.71I and .sup.72I/.sup.73I and the concentration values for lithium determined using these two ratios were in close agreement with each other. The use of heavier molecular ions resulted in a precision of better than 0.1% for the concentration of lithium in .sup.6Li spike determined by R-IDMS and .sup.7Li enriched solution of Li.sub.2CO.sub.3 determined using the pre-calibrated .sup.6Li spike.