engleski

Voltammetry of dissolved iron(III) - nitrilotriacetate - hydroxide system in water solution

The investigation of the dissolved iron(III) - nitrilotriacetate - hydroxide system in the water solution (I = 0.1 mol L-1 in NaClO4 ; pH = 8.0+-0.1) using differential pulse cathodic votammetry, cyclic voltammetry, and sampled direct current (d.c.) polarography, was carried out on a static mercury drop electrode (SMDE). The dissolved iron(III) ion concentrations varied from 2.68×10-6 to 6×10-4 mol L-1 and nitrilotriacetate concentrations were 1×10-4 and 5×10-4 mol L-1. By deconvoluting of the overlapped reduction voltammetric peaks using Fourier transformation, four relatively stable, dissolved iron(III) complex species were characterized, as follows: [Fe(NTA)2]3-, mixed ligand complexes [FeOHNTA]- and [Fe(OH)2NTA]2-, showing a one-electron quasireversible reduction, and binuclear diiron(III) complex [NTAFeOFeNTA]2-, detected above 4×10-4 mol L-1 of the added iron(III) ions, showing a one-electron irreversible reduction character. The determination of the electrochemical parameters of the mixed ligand complex [FeOHNTA]-, such as: transfer coefficient a, rate constant (ks) and formal potential (Eo') was done using a sampled d.c. polarography, and found to be 0.46+-0.05, 1.0+-0.3×10-3 cm s-1, and -0.154+-0.010 V, respectively. Although known previously in the literature, these four species have now for the first time been recorded simultaneously, i.e. proved to exist simultaneously under the given conditions.

iron(III); nitrilotriacetate; hydroxide; speciation; voltammetry; water solution

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