Silica-modified electrode for the selective detection of mercury

Pure silica particles were dispersed within carbon paste and the resulting modified electrode was applied to the selective voltammetric detection of m ercury(ll) species after their accumulation at open circuit. The remarkable selectivity observed between pH 4 and 7 was attributed to the intrinsic ad sorption mechanism which involves a condensation reaction between mercury(I I) hydroxide and hydroxyl groups on the silica surface, leading to the form ation of an inner-sphere-type surface complex. After optimization with resp ect to the electrode composition, the detection medium, and the voltammetri c scan mode, a linear response was obtained in the concentration range betw een 2x10(-7) M to 1 x 10(-5) M, by applying anodic stripping square wave vo ltammetry. Various silica samples were used and their sorption behavior was discussed in relation to their specific surface area and porosity. The eff ect of chloride and pH on the accumulation of mercury(II) on silica was als o investigated.