The potentiometric titration method was used for quantitative determination of germanium sulfide and germanium mercaptide evolved during the sol-gel processing of GeS2 from germanium ethoxide and H2S. The titrations were performed in 2-propanol or in a 50-50 vol.% mixture of 2-propanol and toluene. The ion selective Ag/Ag2S electrode was used for equivalence point detection. Study of the Nernst equation shows that complexes were formed at the electrode surface. However, the titration equivalence point volume clearly demonstrates the formation of Ag2S and Ge(SAg)(n). In order to explain this discrepancy, a new electrode reaction mechanism is suggested and a modified Ag/Ag2S electrode potential equation is proposed.