Volume 46, Number 5  (September - October 2001)

Key words:  mercury, complexometry, thioglycollic acid

A complexometric method for the determination of mercury in the presence of  other metal ions based on the selective masking ability of thioglycollic acid towards mercury is described. Mercury(II) present in a given sample solution 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 xylenol orange as indicator. A known excess of thioglycollic acid solution (1 %) is then added, the mixture is shaken well, and the EDTA released from the Hg-EDTA complex is titrated againts standard lead nitrate solution. Reproducible and accurate results are obtained  for 1.6-80 mg of mercury with relative error 0.7 % and standard deviation <= 0.1 mg. The interference of various ions was studied. This method was applied to the determination of mercury(II) in its alloy compositions.