Spectrophotometric determination of trace amounts of thorium in lanthanum oxide

Abstract

A spectrophotometric method for the determination of trace amounts of thorium in lanthanum oxide or lanthanum metal has been developed.

The method is based on the determination of thorium with thoron after its separation from lanthanum by extraction with a mixture of ethyl acetate and acetone. The efficiency of the separation was tested with a lanthanum-140 tracer. Other elements present in lanthanum oxide as impurities do not interfere.

Thorium contents down to 10 p.p.m. can be determined in a 1-g sample with 1-cm cells used for absorbance measurement. Errors of determination are within the range ±5 per cent. The relative standard deviations on samples containing 30 and 100 p.p.m. of thorium are 1·6 and 1 per cent., respectively.