Potentiometric Determination of Silver Thiolate Formation Constants Using a Ag2S Electrode

Formation constants for silver thiolates were obtained by titration of the ligand in a constant temperature, ionic strength and pH medium and measuring the potential change at a Ag2S electrode. A non-linear equation was derived from which the first and second silver formation constants, β1 and β2', and the sulfide group acid dissociation constant, Ka', were determined. An overall estimate of the uncertainty in the derived parameters was obtained using a Monte Carlo approach. The procedure was compared to a previous work on AgHS°. Log β1', log β2' and - log Ka' results were obtained for cysteine (11.9 ± 0.5, 15.2 ± 0.4, 7.8 ± 0.1), glutathione (12.3 ± 0.3, 14.3 ± 0.8, 8.8 ± 0.3) and 3-mercaptopropanoic acid (12.0± 0.4, 14.0 ± 0.4, 10.5 ± 0.3) at 20 °C and 0.01 m ionic strength.[PUBLICATION ABSTRACT]