Research Of Analysis Method For Rare Earth Impurities In Lanthanum Oxide By LA-ICP-MS

Because of its excellent optical and electrical properties, lanthanum oxide has been broadly applied in high-tech materials, but rare earth impurities can affect its physical and chemical properties, so the content of these elements must be measured. As a new type of solid direct injection analysis techniques, laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS) can largely reduce part of the polyatomic ions injected by solution. However, the current LA-ICP-MS method is mainly applied to the analysis of geological and steel samples because they have solid standards, and application of testing rare earths has not been reported.In this article, the content of rare earth impurities in lanthanum oxide was analyzed by LA-ICP-MS, when lanthanum oxide powder was milled uniformly with microcrystalline cellulose and tabletted. In order to tablet successfully and obtain stable signals, tabletting conditions were explored. The optimum mass ratio of lanthanum oxide and microcrystalline cellulose is 92 to 8, the mixed powder should be milled for at least 15 minutes, and the pressure of tabletting machine select 20 Mpa. Line scanning mode was required to obtain sensitive and stabile signal, and laser ablation parameters were optimized. Finally, 750 V for laser ablation energy, 150μm for spot size, 20 Hz for laser pulse frequency, 60μm/s for scanning rate, and 400 m L/min for helium flow rate are selected. Calibration curves were established using lanthanum oxide standard and the 138 La as internal standard, quantitative analyzed the content of 14 rare earth impurities in three different purity lanthanum oxide samples. After internal calibration, the linear correlation coefficient of each element reached 0.9966 to 0.9999, significantly better than pre-correction. The detection limit of each element were between 0.01 and 0.15μg/g, the quantification limit were between 0.03 and 0.51μg/g. The relative standard deviations were from 1.5% to 5.8%, which indicated an excellent precision. Using t-test to compare the determination results of LA-ICP-MS with ICP-MS, it showed that there’s no significant difference between two methods, which indicated a favorable accuracy. NIST612 glass standard and GBW02901 yttrium oxide reference material were used respectively as calibration materials to analyze part of lanthanum oxide standards and samples. There were significant differences in the results of LA-ICP-MS with standard samples value or ICP-MS value, indicating that if standard samples do not match the sample matrix, the analysis results are not reliable within a certain range of content. Using signal normalization, the LA-ICP-MS analytical method of determine the rare earth impurities in 5N lanthanum oxide was established, and the measurement results with the ICP-MS was basically the same order of magnitude, which achieved a semi-quantitative analysis in high purity lanthanum oxide sample.The results show that laser ablation solid sampling technique can directly determine cerium in lanthanum oxide without correction equation, which can be an important supplementary means for rare earth impurities detection in lanthanum oxide. Research ideas in this paper provide a reference for laser ablation sampling analysis in other rare earth oxides. Meanwhile, it is worth learning for the determination of powders and non-conductor samples by laser ablation inductively coupled plasma mass spectrometry.