1990 Volume 38 Issue 5 Pages 253-259
To develop a reliable method for mass spectrometric determination of rubidium isotopic ratios, four rubidium chemical forms of nitrate, sulfate, chloride, and iodide prepared from an isotopic standard sample NBS-SRM984 were examined using a double-filament thermal-lonization ion souce. The deviation between the observed isotopic ratio and the true value was seen in each sample and shown to decrease with increasing in the mass of counter ion, except sulfate. The deviation were explained as the isotopic fractionation effect in evaporation of the samples based on a theoretical equation given by Kanno. Conclusively, among the tested salts, rubidium iodide has been selected as the best chemical form with the high stability in the mesured values of isotopic ratios.
