Precise Purity Analysis of High-Purity Lanthanum Oxide by Gravimetric Analysis Assisted With Trace Elemental Analysis...

Gravimetric analysis was used to determine the purity of high-purity La₂O₃ by stepwise conversions of the weighing forms. In this study, lanthanum in the sample was converted to La oxalate, La₂O₃, and La₂(SO₄)₃ to evaluate the stoichiometry of the weighing forms for accurate gravimetric determination. The losses of La in the filtrate, the washing solution of the precipitate, and the mechanical loss of La during filtration were measured using inductively coupled plasma optical emission spectrometry. The weighing forms were evaluated by comparing the observed mass ratio with the theoretical value at each conversion step. The final converted La₂(SO₄)₃ was consistent with the theoretical composition based on the observed mass ratio of La₂(SO₄)₃/La₂O₃. Additionally, impurities in the high-purity La₂O₃ were determined by inductively coupled plasma tandem mass spectrometry. The purity of the original La₂O₃ sample was precisely determined to be 99.977 % ± 0.057% (mass fraction as La₂O₃; the value following "±" indicates the expanded uncertainty with a coverage factor k = 2.18) by a combination of the gravimetric analysis using the precipitation from the homogeneous solution method and verification of the weighing forms for La compound.