Croatica Chemica Acta, Vol. 79 No. 1, 2006.
Original scientific paper
Electrochemical Characterization of Iron(III)–Glycine–Nitrilotriacetate Mixed Ligand Complexes and Their Stability in Aqueous Solutions
Vlado Cuculić
Ivanka Pižeta
Abstract
Electrochemical characterization of iron(III)–glycine–nitrilotriacetate (iron(III)-Gly-NTA) mixed ligand complexes and determination of their stability constants and retention time in aqueous solutions (I = 0.1 mol dm–3 in NaClO4, pH = 8.0±0.1 at 25±1 °C), using differential pulse cathodic voltammetry (DPCV), cyclic voltammetry (CV) and direct current (d.c.) polarography with a static mercury drop electrode (SMDE), were performed. Iron(III) concentrations were varied from 5×10–6 to 6×10–4 mol dm–3, NTA total concentrations varied from 2×10–5 to 1×10–3 mol dm–3 and glycine total concentrations were 0.2, 0.02 and 0.002 mol dm–3. Iron(III) redox reaction in the mixed ligand system (by the techniques employed) was found to be a one-electron reversible process. At total concentration ratios of 1 : 800 : 2 for iron(III), glycine and NTA, respectively, the iron(III)-Gly-NTA mixed ligand complexes were dissolved and stable (>18 hours) in the aqueous solution. The complexes were formed either by the addition of NTA into the iron(III) and glycine aqueous solution or by the addition of iron(III) to the mixture of glycine and NTA. Under these conditions, iron(III) hydrolysis was highly suppressed. By fitting of experimental data, the following stability constants for mixed ligand complexes, not found in the literature so far, in 0.1 mol dm–3 NaClO4 aqueous solution were calculated: for iron(III) log β1([FeGlyNTA]) = 27.23±0.69, log β2([Fe(Gly)2NTA]2–) = 30.29±0.77; for iron(II) log β 1([FeGlyNTA]2–) = 14.13±0.43 and log β 2([Fe(Gly)2NTA]3–) = 18.51±0.51.
Keywords
iron(III); mixed ligand complexes; nitrilotriacetate (NTA); glycine; stability constants; voltammetry; aqueous solution
Hrčak ID:
2600
URI
Publication date:
22.4.2006.
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