Titrimetric microdetermination of silver, lead and cadmium with thioglycollic acid and of mercury(II) with 2-mercaptopropanoic acid

A simple and rapid titrimetric method is described for the microdetermination of Ag(+), Cd(2+) and Pb(2+), based on their formation of mercaptides with a measured excess of 2-mercaptopropanoic acid, and similar determination of Hg(2+) with thioglycollic acid. Univalent and bivalent metal ions release one and two thiol protons respectively, which along with the carboxyl protons of the thiol reagent are titrated with standard alkali. The difference from the blank titration gives the increase in acidity which is a function of the metal-ion concentration. The proposed procedure is applicable to samples containing 0.025-0.25 mmole of these ions, the average deviation being in the range 0.2-0.5%.