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Voltammetry of Dissolved Iron(III)–Nitrilotriacetate–Hydroxide System in Water Solution
Author(s) -
Cuculić Vlado,
Pižeta Ivanka,
Branica Marko
Publication year - 2005
Publication title -
electroanalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 128
eISSN - 1521-4109
pISSN - 1040-0397
DOI - 10.1002/elan.200403342
Subject(s) - chemistry , hydroxide , polarography , electrochemistry , inorganic chemistry , cyclic voltammetry , voltammetry , stability constants of complexes , ion , reaction rate constant , differential pulse voltammetry , electron transfer , ligand (biochemistry) , analytical chemistry (journal) , aqueous solution , electrode , kinetics , chromatography , biochemistry , physics , receptor , organic chemistry , quantum mechanics
The investigation of the dissolved iron(III)–nitrilotriacetate–hydroxide system in the water solution ( I =0.1 mol L −1 in NaClO 4 ; pH 8.0±0.1) using differential pulse cathodic voltammetry, cyclic voltammetry, and sampled direct current (DC) 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) 2 NTA] 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 calculations with the constants from the literature were done and compared with the potential shifts of the voltammetric peaks. Fitting was obtained by changing the following literature constants: log β 2 ([Fe(NTA) 2 ] 3− ) from 24 to 27.2, log β 1 ([FeNTA] − ) from 8.9 to 9.2, log β 2 ([Fe(NTA) 2 ] 4− ) from 11.89 to 15.7 and log β 2 ([Fe(OH) 2 NTA] 3− ) from 15.63 to 19. The determination of the electrochemical parameters of the mixed ligand complex [FeOHNTA] − , such as: transfer coefficient ( α ), rate constant ( k s ) and formal potential ( E °') was done using a sampled DC 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.