Application of the Parabolic Model, Specific Ion Interaction, and Debye−Hückel Theories for the Complexation of Dioxovanadium(V) with Ethylenediamine-N,N′-diacetic Acid

Interaction between dioxovanadium(V) and ethylenediamine-N,N′-diacetic acid (EDDA) has been investigated by potentiometric and UV spectrophotometric measurements in an aqueous solution of pH = 1.00 to 2.50 at I = (0.1 to 0.9) mol·dm−3 (NaClO4) and 25 °C. Different speciation models were used to detect the species, but the model that best fits the experimental data takes into account the formation of two species, VO2H2L+ and VO2HL. Distribution diagrams for the main species at different ionic strengths have been calculated as a function of pH. The dependence on ionic strength of the stability and dissociation constants was studied by using the extended Debye−Hückel-type equation (EDH), specific ion interaction theory (SIT), and the parabolic model. All of these approaches gave comparable and satisfactory results. Literature data were also considered and compared.