Normal Pulse Polarographic Study of the Electrode Reaction of Copper(II) Complexes with Ethylenediaminetetraacetic Acid(EDTA) and N-(2-Hydroxyethyl)ethylenediamine-N,N′,N′-triacetic Acid(HEDTA)

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Abstract
The normal pulse polarographic behavior of the Cu(II)–EDTA and –HEDTA complexes was examined in a wide range of pH values to elucidate the mechanisms of their electrode reactions and to evaluate the relevant electro chemical kinetic parameters. From analysis of the dependence of the half-wave potentials on the sampling time and the hydrogen ion concentration, it was shown that the reduction wave of the Cu(II)–EDTA complexes observed in the pH range of 2.0 to 9.5 at −0.1 to −0.5 V vs. SCE corresponds to the simultaneous reduction of four complex species, CuH3L+, CuH2L0, CuHL−, and CuL2−, where CuHpL(p−2)+ and L4− denote the protonated complex species with p protons and the unprotonated EDTA ion, respectively. The reduction wave of the Cu(II)–HEDTA complexes in the pH range of 3.0 to 9.0 at −0.25 to –0.4 V vs. SCE corresponds to the simultaneous reduction of two complex species, CuHL0 and CuL−, where L3− denotes the unprotonated HEDTA ion. The kinetic parameters of the corresponding complex species (i.e. the cathodic transfer coefficient and the standard rate constant of electrode reaction) were evaluated.

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