Complexometric Determination of Mercury(II) Using 2-Mercaptopropionylglycine as a Selective Masking Reagent

A selective complexometric method for the determination of mercury(II) in the presence of associated metal ions is reported, based on the selective masking ability of 2-mercaptopropionylglycine (MPGH₂) towards mercury. Mercury, along with other associated metal ions, is first complexed with excess of EDTA and the surplus EDTA is back titrated at pH 5-6 (hexamine buffer) with standard zinc sulfate solution using xylenol orange as indicator. An aqueous 1% solution of MPGH₂ is then added to displace EDTA selectively from the Hg-EDTA complex and the released EDTA is titrated with the same standard zincsulfate solution. Reproducible and accurate results are obtained for 4-85 mg of mercury with a relative error of ≤0.26% and coefficient of variation not exceeding 0.42%. The interferences of various cations and anions are studied. The method is used for the analysis of mercury in its complexes and alloy samples.