Photometric determination of thorium and zirconium in a mixture of the two. Use of arsenazo III

Abstract

A spectrophotometric method is described for the determination of both thorium and zirconium with arsenazo III. In 3N hydrochloric acid containing oxalic acid, thorium alone forms a colored complex with the reagent. The absorbance is measured at 665 mμ. In 9N hydrochloric acid containing gelatin, both thorium and zirconium form colored complexes. The absorbance of the 9N hydrochloric acid solution at 665 mμ is equal to the sum of the absorbances of the thorium and zirconium complexes.
Therefore, zirconium can be determined by difference. Satisfactory results were obtained with 530 μg of thorium and 510 μg of zirconium in a volume of 25 ml or with weight ratios of Th/Zr ranging from 0.5 to 6.