DETERMINATION OF RARE-EARTH ELEMENTS IN HIGH-PURITY RARE-EARTH-OXIDES BY LIQUID-CHROMATOGRAPHY, THERMIONIC MASS-SPECTROMETRY AND COMBINED LIQUID-CHROMATOGRAPHY THERMIONIC MASS-SPECTROMETRY

A high-performance liquid chromatographic (HPLC) method for the determination of rare earth elements in rocks has been modified and used for the determination of rare earth elements (REE) in high purity rare earth oxides. The detection limit was 1-1.5 ng or 2-3 mg/kg when a solution corresponding to 0.5 mg of the rare earth oxide was injected. The REE determination was also carried out by adding a mixture of selected REE isotopes to the sample and analysing the collected HPLC-fractions by mass spectrometry (MS) using a thermionic source. Since the matrix element was not collected, interference from this element during the mass spectrometric analysis was avoided. Detection limits as low as 0.5 mg/kg could then be obtained. Detection limits as low as 0.05 mg/kg were possible by MS without HPLC-pre-separation, but this approach could only be used for those elements that were not affected by the matrix. Commercial samples of high purity Nd2O3, Gd2O3 and Dy2O3 were analysed in this study, and a comparison of results obtained by HPLC, combined HPLC/MS and direct MS are presented.