VOLTAMMETRIC DETERMINATION OF TRACE MERCURY IN CHLORIDE MEDIA AT GLASSY-CARBON ELECTRODES MODIFIED WITH POLYCATIONIC IONOMERS

The perfluorinated polycationic polymer Tosnex(R) is used for preparin g polymer modified electrodes able to preconcentrate and detect the an ionic complex HgCl42-, which is the prevailing inorganic Hg(II) specie s in sea water and other chloride media. The study of the ion-exchange voltammetric behaviour of the tetrachloromercurate(II) complex at Tos flex-modified electrodes indicates the efficient incorporation of the analyte into the polymeric coating to which a remarkable positive shif t in the reduction potential of HgCl42- to Hg-0 is associated. The par tition and selectivity coefficient values for the ion-exchange equilib rium involved are calculated from voltammetric data. When using an ion -exchange preconcentration step under open circuit conditions followed by a cyclic voltammetry detection step, a detection limit in the 10(- 8) M range is achieved, the exact figure depending on the scan rate em ployed. The application of a reducing potential during the preconcentr ation (i.e., using a mixed ion-exchange + Faradaic preconcentration re gime) and the use of differential pulse voltammetry, lower the relevan t detection limit by about three orders of magnitude. Results concerni ng optimization of the experimental parameters as well as lowering of the influence of possible interferents, such as copper and competing a nions, are reported. Finally, an analytical procedure for exploiting t he peculiar properties of Tosflex-modified electrodes for the determin ation of mercury in coastal waters samples is proposed and experimenta lly tested.