Acid-base equilibria of captopril and its complex -formation with iron (II) and zinc (II) have been investigated in aqueous medium and ionic strength (I=0.1 M sodium perchlorate) conditions.Protonation constant of the ligand and the stability constants of 1:2 metal-ligand complexes formed were determined from the obtained potentiometric data.The complexes of Fe (II) and Zn (II) with captopril (cap...