Ferrocene spiked carbon paste electrode and its application to electrocatalytic determination of ascorbic acid

Ferrocene modified carbon paste electrode (FcMCPE) was constructed by incorporation of ferrocene in a graphite powder - paraffin oil matrix. It has been shown by direct Current cyclic voltammetry, double step chronoamperometry and chronocoulometry that this electrode can catalyze the oxidation of ascorbic acid in aqueous buffered solution. It has been found that under optimum condition (pH=5) the oxidation of ascorbic acid at the surface of such an electrode occurs at potential about 220 mV less positive that at an unmodified carbon paste electrode. The value of K-0 for ferrocene/ferrocenium couple was 8.9 x 10(-4) by chronocoulometry method. The catalytic oxidation peak current was linearly dependent on the ascorbic acid concentration and a linear calibration curve was obtained in the range 2.2 x 10(-4) 1.4 x 5 10(-3) M of ascorbic acid with a correlation coefficient of 0.9997. The detection limit (3sigma) was 3.2 x 10(-5).