Taking into account reactivity of reagent, individual degrees of reactions and two-component mixtures of sulfide forming ions, the authors theoretically proved the possibility to use potassium dimethyldithiophosphate in potentiometric titration of some sulfide forming ions. The consecutive order of proceeding of ions reaction was calculated on the base of ionic product of the reagent complexes. Selectivity of possible determination of each ion in the consecutive order of reactions and possibility to titrate two-, three- and four-component mixtures has been predicted. Prognosis of choosing indicator electrodes has been made.