engleski

Revision of iron(III)-citrate speciation in aqueous solution. Voltammetric and spectrophotometric studies

A detailed study of iron(III)-citrate speciation in aqueous solution (θ = 25 °C, Ic = 0.7 mol L-1) was carried out by voltammetric and UV-Vis spectrophotometric measurements and the obtained data were used for reconciled characterization of iron(III)-citrate complexes. Four different redox processes were registered in the voltammograms: at 0.1 V (pH = 5.5) which corresponded to the reduction of iron(III)-monocitrate species (Fe:cit = 1:1), at about -0.1 V (pH = 5.5) that was related to the reduction of (FeL2)5-, (FeL2H)4- and (FeL2H2)3- complexes, at -0.28 V (pH = 5.5) which corresponded to the reduction of polynuclear iron(III)-citrate complex(es), and at -0.4 V (pH = 7.5) which was probably a consequence of Fe(cit)2(OH)x species reduction. Reversible redox process at -0.1 V allowed for the determination of iron(III)-citrate species and their stability constants by analyzing Ep vs. pH and Ep vs. [L4-] dependence. The UV-Vis spectra recorded at varied pH revealed four different spectrally active species: FeLH (log β = 25.69), (FeL2H2)3- (log β = 48.06), (FeL2H)4- (log β = 44.60), and (FeL2)5- (log β = 38.85). The stability constants obtained by spectrophotometry were in agreement with those determined electrochemically. The UV-Vis spectra recorded at various citrate concentrations (pH = 2.0) supported the results of spectrophotometric- potentiometric titration.

iron(III) ; citric acid ; voltammogram ; iron(III)-citrate complexes ; UV-Vis spectra ; stability constants

nije evidentirano