SPECTROPHOTOMETRIC STUDY OF THE REACTION BETWEEN IRON (III) AND KOJIC ACID

Abstract

A method introduced by Vareille enables calculation of formation constants of colored metallic complexes in solution by making appropriate deductions from the presence of isobestic points in the spectra of suitably chosen solutions. The rationale of this method is derived rigorously, and its application extended to include cases where three complexes are present together in certain regions of pH. These principles are applied to derive for the ferric kojates the following formation constants, at 25 °C and ionic strength 0.5: log K1 = 10.16, log K2 = 8.29, log K3 = 6.90. The relationship between pH and pL for the experimental conditions is calculated, thereby enabling the estimation of the distribution of the metal among the several species in each solution and the absorption spectrum of each complex.