Oscillatory chemical reaction as a sensor of Cu(II)-EDTA complex formation and ligand degradation in copper ion-catalyzed oxidation of thiocyanate ions with hydrogen peroxide

The complex dynamics of the homogeneous H2O2-NaSCN-CuSO4-NaOH oscillator is influenced by the addition of EDTA, which manifests itself in the modification or complete suppression of the oscillations. However, depending on EDTA concentration, this effect can be reversible or not. Potentiometric and spectroscopic studies of these phenomena, together with recent discoveries about possible chemical interactions and compound formation in the Cu(II)-H2O2-EDTA system, resulted in the development of a new kinetic mechanism of the complex interaction of EDTA with this oscillatory system. The model involves 13 intermediates and is an extension of our former, 10-variable mechanism of the H2O2-NaSCN-CuSO4-NaOH oscillator. Reliability of the proposed reaction scheme has been confirmed by numerical calculations, enabling also the estimation of appropriate reaction rate constants. The work is an example of the application of the chemical oscillatory reaction to study qualitatively and quantitatively the interactions of foreign species with the components of positive and negative feedback loops of a chemical dynamical system.