Indirect complexometric determination of mercury(II) using thioglycollic acid as a masking agent

A complexometric method for the determination of mercury in the presence of other metal ions based oil the selective masking ability of thioglycollic acid towards mercury is described. Mercury(II) present in a given sample so lution is first complexed with a known excess of EDTA and the surplus EDTA is titrated against lead nitrate solution at pH 5.0 6.0 (hexamine) using xy lenol orange as indicator. A known excess of thioglycollic acid solution (1 %) is then added, the mixture is shaken well, and the EDTA released from th e Hg-EDTA complex is titrated against standard lead nitrate solution. Repro ducible and accurate results arc obtained for 1.6-80 mg of mercury With rel ative error 0.7%. and standard deviation less than or equal to0.1 mg. The i nterference of various ions was studied. This method was applied to the det ermination of mercury(II) in its alloy compositions.