Spectrophotometric determination of equilibrium constants of two mutual competitive reactions by the method of isosbestic points.

We have developed a method that makes use of dual isosbestic points in a dual ligand, single metal system that allows the determination of the equilibrium constants of complexes in which two ligands compete for the same metal ion, and one complex is colourless. The competition of methyl thymol blue and citrate was used to test the model.

Determination of the stability constant of the ternary complex formed in the copper-bipyridyl-eriochrome cyanine R system, by an isosbestic point-spectrophotometric method.

This paper reports a new method for determining the stability constants of ternary complexes, based on analysis of isosbestic points. First, it is necessary to determine the absolute molar absorptivities of the various species concerned, then their concentrations and the stability constant. In this method, the approximate treatment of classical photometric methods is not required. The conditional constant can be calculated directly from the measured data.