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, beta(1)' and beta(2)', and the sulfide group acid dissociation constant, K-a', 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 degrees. Log beta(1)', log beta(2)' and -log K-a' 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 degrees C and 0.01 m ionic strength.