Adsorptive square wave voltammetry of metal complexes. Effect of ligand concentration. Part IV. Experimental applications on Hg-ferron complexes

The theoretical models developed in Part III of this work are employed for the study of the oxidative adsorption of ferron (7-iodo-8-hydroxyquinolin-5-sulphonic acid) on mercury under square wave voltammetric conditions. The fits between experimental and theoretical results indicated that the electrochemical reaction involves the direct transfer of two electrons in solutions with pH < 4.5 whereas the exchange of only one electron has to be considered for solutions with higher pH values. The studies performed by cyclic voltammetry are consistent with the presence of adsorbed species, but they do not give evidence of the variations on the number of exchanged electrons with the solution pH. A general mechanism is proposed to explain the variation of the transferred electrons. The electrochemical rate constants, the charge transfer coefficients and the adsorption constants for the electroactive species were determined for solutions with different pH by fitting voltammograms collected at various square wave amplitudes and frequencies. (C) 2003 Elsevier Science B.V. All rights reserved.