A new method of determination of stability constants for complexes based on isomolar mixtures. 1 - The iron(III)-5-sulfosalicylic acid

A simple and useful method for determination of stability constant from spectrophotometrical data of isomolar mixtures has been developed. It gives several criteria for the control of accuracy of experimental data. The method is illustrated by the system iron(III)-5-sulfosalicylic acid. An equilibrium constant of K = 2.14 +/- 0.07 M and molar absorptivity epsilon = 2200 M-1 cm(-1), at lambda = 498 nm, were determined for 1:1 complex at: 298 K, pH less than or equal to 1.0 and ionic strength mu = 1.0, in agreement with literature data.