Polarographic determination of the stability constants of cadmium and lead ternary complexes with thiosemicarbazide and thiosulphate

The stability constants of binary and ternary complexes of Cd [II] and Pb [II] ions with thiosemicarbazide [TSC] as a primary ligand and thiosulphate [TS] as a secondary ligand have been determined polarographically at 25 degree and micro = 0.13 M [NaNO3]. Cadmium and lead ions individually form 1:1, 1:2 and 1:3 complexes with both ligands. The complexation constants of the mixed species Beta11, Beta12 and Beta21 are calculated. The negative value of Beta12 in the Pb[II] -TSC-TS system indicates the absence of Pb[[TSC] [TS]2][2]