Determination of rare earth impurities in high-purity lanthanum oxide using electrothermal vaporization/ICP-AES after HPLC separation

A new method for determination of trace rare earth impurities in high-purity La2O3 by HPLC combined with electrothermal vaporization inductively coupled plasma atomic emission spectrometry (ETV-ICP-AES) is proposed. The chromatographic retention behaviors of matrix (La) and rare earth impurities were studied using 2-ethylhexyl hydrogen 2-ethylhexylphosphonate (P507) resin as the stationary phase and dilute nitric acid as the mobile phase. It was found that the use of EDTA as an eluent enables effective elution of rare earth impurities from a HPLC column. The influence of EDTA in ETV-ICP-AES was also discussed. The experimental results showed that a favorable separation between matrix (La) and rare earth impurities could be obtained within 30 min. The method proposed has been applied to the analysis of high-purity La2O3; the results obtained were in good agreement with those obtained by ICP-MS. Under the optimum conditions, the detection limits (DLs) for 14 rare earth elements (REEs) were in the range of 0.8 ng/ml (Yb) to 48 ng/ml (Ce). The recoveries of 14 REEs were in the range of 90% to 110%.