Spectrographic determination of trace rare earth elements in high purity thorium

An emission spectrographic determination of fifteen rare earth elements in thorium was developed, the spectrographic procedure was carried out using low current d.c. arc and using Sc as an internal standard. The rare earth impurities were concentrated with cation-exchange resin. Very high sensitivity was achieved with 1 g sample. The detection limits range from 0.01 μg for Yb to 0.5 μg for Pr and Nd.