ION-EXCHANGE VOLTAMMETRY OF TRACE MERCURY(II) AT GLASSY-CARBON ELECTRODES COATED WITH A CATIONIC POLYPYRROLE DERIVATIVE - APPLICATION TO PORE-WATERS ANALYSIS

Glassy carbon electrodes modified with coatings of poly-[1-methyl-3-(p yrrol-1-ylmethyl)pyridinium], poly-MPP, were prepared by electrochemic al oxidation of the suitable monomer in acetonitrile solutions. The an ion exchange properties of the coated electrode were exploited in aque ous solutions for preconcentrating and detecting the anionic complex H gCl42-, which is the prevailing inorganic Hg-II species in seawater an d other chloride media. The partition coefficients for the ion-exchang e equilibrium involved were calculated from voltammetric data and comp ared with those obtained at electrodes coated with Tosflex, a perfluor inated anion exchanger, and poly(vinylpyridine). The selectivity of th e poly-MPP coated electrodes towards the rejection of copper interfere nce was also studied. The optimization of experimental conditions allo wed the development of a differential pulse voltammetric method for th e determination of submicromolar mercury concentrations with a detecti on limit of 0.1 nM. The method was applied to the analysis of mercury in the pore-waters of tidal sediments of the Lagoon of Venice (Italy), determining Hg-II concentration values in the 70-80 nM range.