Complexometric determination of mercury(II) using 2-thiobarbituric acid as a releasing agent

A simple and selective complexometric method for the determination of mercury is proposed, based on the selective releasing ability of 2-thiobarbituric acid towards mercury(II). Mercury(II) present in a given sample solution is first complexed with an excess of EDTA and the unreacted EDTA is titrated against zinc sulphate solution at pH 5-6 (hexamine buffer) using xylenol orange as the indicator. An excess of a 0.25% solution of 2-thiobarbituric acid is then added to displace EDTA from the Hg(II)-EDTA complex. The released EDTA is estimated. Reproducible and accurate results are obtained for 3-95 mg of mercury(II) with coefficient of variation not more than 0.34%. The effects of various ions were studied. The method is used for the analysis of mercury in its synthetic alloy mixtures and also in complexes.