Selective complexometric determination of mercury using 4-amino-5-mercapto-1,2,4-triazole as masking reagent

Mercury and other ions are complexed with an excess of EDTA and the excess EDTA is titrated with ZnSO4 solution at pH 5.0-6.0 using xylenol orange as indicator. An excess of alcoholic solution of 4-amino-5-mercapto-1,2,4-tria zole is then added to decompose the Hg-EDTA complex and the released EDTA i s titrated with standard ZnSO4 solution. Accurate results have been obtaine d for 1.86-74.46 mg of mercury with relative error of <0.39 and standard de viation <0.04 mg. The method has been successfully applied for the analysis of Hg in synthetic alloy solutions.