Voltammetric investigation on sulfide ions in aqueous solutions with mercury-coated platinum microelectrodes Original Research Article

The general voltammetric behavior of mercury-coated platinum microelectrodes in sulfide solutions has been investigated. The formation of an HgS film and its reduction process have been studied as a function of the analytical concentration of sulfide and pH. In general, the mercury microelectrodes has displayed a good reproducibility and high stability even in solutions containing high sulfide concentrations. For the analytical determination of sulfide, the reduction process of the HgS formed at the mercury surface has been considered. The voltammetric features of the cathodic peak as a function of total sulfide concentration, pH and deposition time have been studied in detail. It has been found that the peak potential shifts towards the more negative potentials, as the analytical concentration of sulfide and pH increase. In some cases, a split of the cathodic peak has been observed, depending on the effective deposition time employed in the accumulation of HgS onto the electrode surface, as well as on the scan rate. Calibration curves have been performed over the concentration range 1–20 μM and a good linearity has been observed for the cathodic stripping charge against concentration plot, with a sensitivity of 0.135 nC/μM. Using the linear sweep voltammetry in the cathodic stripping step, a detection limit of 0.25 μM has been found.