Complexometric determination of thallium(III) using sodium sulfite as a selective releasing agent

Abstract

A complexometric method for the determination of thallium(III) in the presence of other metal ions is described. This is based on the selective masking ability of sodium sulfite towards thallium(III). At pH 5.0–6.0, hexamine, thallium(III) and other diverse metal ions (e.g., common metal ions, including copper, and rare earth elements) are initially complexed with an excess of EDTA. The surplus EDTA is titrated with zinc sulfate solution, using Xylenol Orange as indicator. An excess of sodium sulfite solution (1% m/v) is then added, the mixture is shaken well and EDTA, released from the TI–EDTA complex, is titrated against standard zinc sulfate solution. The method works well in the range 4–80 mg of thallium(III), with a relative error ⩽0.3%. The method is applied to the determination of thallium(III) in its alloy compositions and in its complexes.