Determination of uranium, thorium and lanthanum in mixed solutions using simultaneous spectrophotometry

A simultaneous spectrophotometric method was developed for assay of uranium, thorium and lanthanum in mixed solutions by absorbance measurements of their arsenazo III complexes at appropriate wavelengths in three different solutions. The absorbances were additive for the three metals in each solution. The values of the molar absorption coefficients were obtained by a least-squares fit of the data of absorbance against the concentration of standard metal solution, individually. The concentration of each metal in a mixed solution was calculated separately from simultaneous equations. The error of the method was within 5%.