Accuracy of theoretical equations for diffusion currents at a disk electrode

The uncertainty of the most accurate and convenient theoretical equation for the diffusion current at a disk electrode now available, the Shoup-Szabo equation, was found experimentally. The diffusion coefficient and the concentration of the electroactive species were calculated from the two adjustable parameters of the equation that were obtained by curve fitting of the observed chronoamperogram to the equation. The value of the concentration obtained differed from the actually known value, and the difference between these two values changed according to the time region of the chronoamperogram analyzed. The maximum deviation from its known value of the concentration obtained was ±3%. The dummy data obtained from the results of the digital simulation of this problem gave similar results. The most uncertain part of the equation covered the time region of the usual chronoamperogram taken by a μm- or mm-sized disk electrode.