Determination of lanthanum in rare earth oxide mixtures by X-ray fluorescence

Lanthanum in rare earth oxide mixtures was determined by three X-ray fluorescence methods : addition method, direct comparison method, and internal standard method. By the last method with barium as internal standard, lanthanum and cerium could be determined simultaneously with no influence of co-existing thorium. The results obtained by the above three methods were in good agreement with one another. The validity of the lanthanum contents thus determined was supported by the results of lanthanum oxide addition experiments and of chemical analysis of cerium, as well as by the consideration on the "infinitely diluted state."