Indirect Complexometric Determination of Bismuth Using 2-Mercaptoethanol as Masking Agent

 A new method for the complexometric determination of Bi in the presence of co-ions using 2-mercaptoethanol as selective masking agent has been proposed. Bismuth along with other ions in a given sample solution are initially complexed with excess of EDTA. The pH of the solution is adjusted to 5.0–6.0 using solid hexamine (10 ± 2 g) and the remaining uncomplexed EDTA is titrated with lead-nitrate solution using xylenol orange indicator. A known excess of 2-mercaptoethanol solution (5% alcoholic) is then added, the mixture is shaken well and the released EDTA from the Bi(III)-EDTA complex is titrated against standard lead-nitrate solution. The method is applied to the determination of bismuth in Wood’s alloy. Reproducible and accurate results are obtained for 2–40 mg of bismuth with relative errors ≤ 0.5% and standard deviations ≤ 0.04 mg. Received January 15, 1999. Revision March 29, 1999.