Determination of methylmercury at Nafion coated electrodes by single and multiple pulse voltammetric techniques

The voltammetric behaviour of methylmercury at Nafion coated glassy carbon electrodes is examined. Cyclic voltammograms recorded at coated electrodes show a dramatic increase of peak currents with respect to bare electrodes, this effect being more evident in perchlorate supporting electrolytes rather than in chloride containing media. Experimental evidence indicates that ion-exchange preconcentration of the cation CH3Hg+ is the prevailing process, even if the incorporation of neutral species such as CH3HgCl by hydrophobic interactions cannot be neglected. The application and optimization of pulsed techniques like differential pulse voltammetry and Osteryoung's square wave voltammetry, indicates the possibility to use Nafion coated electrodes for the determination of trace methylmercury at submicromolar levels. The analytical performances can be further improved by using, at the Nafion coated electrode, a multiple pulse technique named multiple square wave voltammetry. The application and optimization of this technique to the system under investigation is presented and discussed.