Arsenazo III-spectrophotometry for the determination of thorium content

The complexation interaction between arsenazo III chromogenic agent and tetravalent thorium ion (Th4+) is the theoretical basis for the determination of thorium by spectrophotometry. In this paper, the effects of the acidity, temperature, interfering ions and Th4+ concentration on the absorbance and stability of arsenazo III-Th4+ solution by spectrophotometry were systematically studied. The results showed that the solutions to be tested had high absorbance values and stability only when the concentration of hydrochloric acid was greater than 6 mol·L−1. The absorbance decreased only 0.02 when the temperature was changed from 15°C to 40°C. The absorbance of arsenazo III-Th4+ solution at 662 nm showed a good linear relationship with the concentration of Th4+ under the same experimental environment (R2 = 0.9986), and the apparent molar absorption coefficient was 9.95 × 104 L·mol−1·cm−1, showing that thorium can be accurately quantitatively measured according to the Lambert-Beer law under these conditions.