Photochemical reduction of phenosafranine by edta and its use in amperometric titrations

Abstract Phenosafranine in the presence of ethylenediaminetetraacetic acid is reduced to the leuco dye form on illumination with white light. The rate of photoreduction is strongly pH-dependent and exhibits a maximum at about pH 6. Variables such as wavelength and intensity of the light and the concentration of reactants have been studied. The photoreduction involves a long-lived excited state of the dye and is retarded by small amounts of p -phenylenediamine and iodide. The dye is used as an amperometric indicator in titrations of Pb(II), Zn(II) and Cu(II) with EDTA; the method is applicable in the range 0.02–0.0005 M . The current is caused by anodic oxidation of the phenosafranine reduced in the photochemical reaction with EDTA.