Numerical simulations of linear scan anodic stripping voltammetry at a modified square array of hemispherical microelectrodes located in a thin-layer cell

摘要

The finite element method has been used to simulate LSASV measurement at a loosely packed square array of recessed microdiscs and of hemispherical mercury microelectrodes located in a thin-layer cell. The mercury volume (radius = 7.5 μm), the protective gel (thickness = 300 μm) and the solution medium (thickness = 200 μm) have been meshed. The concentrations of the reduced and oxidised species were linked both by the Nernst equation and the equality of the fluxes at the mercury|gel interface. Both overlapping of adjacent diffusion layers and depletion occurring in this finite box decrease the amount of species being reduced during the deposition step. However, the peak width (W~(1/2) = 39 mV) and peak potential (E_p - E'~0 = -34.6 ± 1 mV) of the resulting stripping current are independent of the deposition time. During the stripping step, the metal concentration at the surface of the electrode is much higher than the initial concentration. The time to reach a uniform concentration in the gel again after the voltammetric reoxidation step has been determined, for both single microelectrode and a square array, as a function of the deposition time, thus giving the maximum frequency of successive measurements that should be used. Agreement between simulated and experimental results confirms that diffusion is the predominant transport process occurring in such thin-layer cell. In addition, comparison with analytical expressions has been done whenever possible.