Complexometric determination of cadmium using 2-Mercaptoethanol as masking reagent

A complexometric method for the determination of cadmium(II) in presence of other metal ions is described based on the selective masking ability of 2-mercaptoethanol towards cadmium(II). Cadmium and other ions in a given sample solution are initially complexed with excess of EDTA and the surplus EDTA is titrated with lead nitrate solution at pH 5.0–6.0 (hexamethylentetramine), using xylenol orange as indicator. A known excess of 2-mercaptoethanol solution (10% alcoholic) is then added, the mixture is shaken well and the released EDTA from the Cd-EDTA complex is titrated against standard lead nitrate solution. The interferences of various ions are studied and the method is applied to the determination of cadmium in its complexes. Reproducible and accurate results are obtained for 3.5–25mg of Cd with relative errors 0.65% and standard deviations 0.06 mg.