Polarography investigations have been carried out on the ternary complexes formation of In(III) with Phthalic acid and Histidine at different concentrations of weak ligand (Phthalic acid) at 298 K temperature. The complexes have been studied polaro graphically at the DME,m = 1M (kcl). The stability constants of In(III)  with phthalic acid and amino acid was determined by method of defordand Hume while the stability constants of mixed ligand complexes have been evaluated by the method of Schaap and mcmasters. The reduction of the system in each case is quasireversible and diffusion controlled involving three electrons. The startical and electrostatic effects have also been discussed by using these stability constants. The mixing constants (Km) and stabilization constant (Ks) were calculated for comparative study of simple and mixed ligand complexes.

Keywords: Polarography Study, In(III),  phthalic Acid, Histidine, Quasireversible Iron, Ternary Complex Diffusion Controlled.

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