Complexometric determination of mercury(II) using thioglycolic acid as indirect masking agent

A simple, rapid and selective complexometric method is proposed for the determination of mercury(II). Mercury(II) and other diverse associated metal ions are first complexed with excess of EDTA and the surplus EDTA is back titrated with standard zinc sulfate solution at pH 5.0-6.0 (hexamine buffer) using xylenol orange as indicator. A 1% aqueous solution of thioglycolic acid is then added to displace EDTA from the Hg(II)-EDTA complex. The released EDTA is titrated with standard zinc sulfate solution as before. Reproducible and accurate results are obtained in the range 5-84 mg of mercury with relative error of less than 0.21% and coefficient of variation (n = 6) not more than 0.34%. The interference of various ions was studied and the method was used for the analysis of mercury in its synthetic alloy mixtures and also in complexes.