Electroanalytical study on the ion-exchange voltammetric behaviour of Hg(II) at tosflex-coated glassy carbon electrodes

The cyclic voltammetric behaviour of HgC! 2- at glassy carbon electrodes coated with a thin film of Tosflex ® IE-SA 48 (a perfluorinated anion exchanger) is studied. Concerning the reduction of HgCl24 - preconcentrated in the coating, a relevant positive shift in reduction peak potentials is observed, both when increasing the HgCI 2- solution concentration and decreasing the scan rate. The analysis of the voitammograms indicates that an irreversible reduction process is occurring. A remarkable positive shift in peak potentials with respect to bare electrodes is also observed. All experimental evidence obtained agrees with the formation of a metal phase, namely Hg °, whose deposition is highly favoured by the presence of the coating, as a consequence both of preconcentration effects and of the decrease in diffusion coefficients related to the ion-exchange incorporation. As far as the reoxidation of deposited Hg ° is concerned, the study of the effect of the scan rate, the anaiyte solution concentration and the loading of chloride anions in the coating indicates that the reversible oxidation to an insoluble calomel deposit occurs at high Hg ° and low CI- loadings. The formation of calomel is confned also by ex situ X-ray diffractometric measurements. On the contrary, low Hg and high CI- loadings within the coating favour the dispmportionation of the calomel formed and the complete regeneration of the modified electrode.