The Determination of the Stability Constants of Mixed Ligand Complexes of Ascorbic Acid, Pyridoxine HCl and Some Amino Acids with Some Metal Ions by Potentiometric Titration Method

A potentiometric titration technique has been used to determine the stability constants for the various complexes of Cu(II), Ni(II), Co(II) with Ascorbic acid, Pyridoxine.HCl (L2)as secondary ligand and selected amino acids (L1) as primary ligands.Ternary complexes of amino acids are formed in a stepwise mechanism, where by (A) binds to Cu(II), Ni(II), Co(II), followed by interaction with ligand (L), whereas the ligands form ternary complexes through a simultaneous mechanism. The formation constants of the complexes were determined at room temperature and ionic strength 0.1 M NaClO₄. The relative stabilities of the ternary complexes are compared with those of the corresponding binary complexes in terms of ΔlogK values. The concentration distributions of the complexes were evaluated.