Formation and Stability of Cadmium(II)/Phytate Complexes by Different Electrochemical Techniques. Critical Analysis of Results

In the present work the stability constants of various cadmium(II)/phytate (Phy) species were determined at T=298.15 K in NaNO₃(aq) at I=0.1 mol⋅L⁻¹ by DP-ASV (Differential Pulse Anodic Stripping Voltammetry) and by potentiometric titrations using an ISE-Cd²⁺. Cyclic voltammograms were also recorded to check the electrochemical behavior of cadmium in the presence of phytate. The results were analyzed together with previous data determined by ISE-H⁺ measurements. Data obtained were used to provide an exhaustive speciation scheme for the phytate/cadmium(II) system at different conditions, as well as a comprehensive representation of the binding ability of phytate toward cadmium(II). Different pL₅₀ values {a previously proposed empirical parameter, expressed as −log ₁₀ C _Phy, where C _Phy is the total phytate concentration necessary to bind 50% cadmium(II)} were also calculated by modeling its dependence on pH.