A simple and rapid complexometric determination of thallium(III) using mercaptoethane as demasking agent

A simple, rapid and selective complexometric method is proposed for the determination of thallium(III), using mercaptoethane(EtSH) as demasking agent. The sample solution containing Tl(III) is first complexed with excess EDTA and the surplus EDTA is removed by titration at pH 5-6 with zinc sulphate solution using xylenol orange as indicator. EtSH solution is then added to displace EDTA selectively from Tl-EDTA complex. Thallium is determined indirectly by titration of released EDTA with zinc sulphate solution. Reproducible and accurate results are obtained in the concentration range 4-80 mg of thallium with a relative error ≤ ±0.6% and relative standard deviation ≤0.7%. The method is successfully applied to the determination of Tl(III) in its synthetic alloy compositions and complexes, and waste-water samples.