An emission spectrographic method is described for the determination of certain rare earths—Ce, Sm, Eu, Gd, Dy, Ho, Er, Yb, and Lu—at fractions of ppm concentration in uranium samples using LiF–AgCl–graphite powder mixture as carrier. The rare earths chemically separated from uranium were excited in a dc arc. Thulium was used as an internal standard. The detection limits in ppm on the basis of 5 g uranium sample are: Yb 0.004; Eu, Gd, Er 0.02; Dy, Lu 0.05; Sm, Ho, 0.2; and Ce 0.5. The precision of the method expressed as a coefficient of variation is estimated to be ±9%. The effect of 14 nonrare earth elements on the intensity of analysis lines was investigated.
B. D. Joshi and B. M. Patel, "Chemical Separation and Spectrographic Determination of Trace Amounts of Rare Earths in Uranium Using LiF–AgCl Carrier," Appl. Spectrosc. 24, 573-576 (1970)