Electrocatalytic response of carbohydrates at copper-alloy electrodes

The voltammetric responses observed for carbohydrates and polyalcohols at ∼0.60 V in 0.10 M NaOH are significantly larger at preanodized CuMn (95:5) electrodes as compared to preanodized pure Cu electrodes. Apparent values for the number of electrons transferred (napp) and the corresponding values of heterogeneous rate constants (kapp) are estimated for selected reactants from the slopes and intercepts, respectively, of Koutecký–Levich plots of background-corrected voltammetric currents obtained at CuMn and Cu rotated disk electrodes (RDEs). Values of napp (and kapp) for sorbitol and glucose are 11.8 (9.2×10−3 cm s−1) and 11.7 (8.0×10−3 cm s−1), respectively, at a CuMn RDE. These are compared to the values 10.4 (1.8×10−3 cm s−1) and 9.6 (2.0×10−3 cm s−1) for sorbitol and glucose, respectively, at a Cu RDE. The larger sensitivities observed at the CuMn RDE in comparison to the Cu RDE are concluded to be the beneficial result of larger kapp values at the alloy electrode. Furthermore, the larger kapp values are speculated to result from enhanced preadsorption of the reactant species at Mn(IV) sites in the preanodized CuMn surface. In flow-injection measurements, the peak signals obtained for successive injections of glucose using a CuMn electrode (0.60 V vs. SCE) were quite stable with a standard deviation of 1.5%. However, large day-to-day variations (±15%) observed in the average peak signals are attributed to the temperature sensitivities of the kapp value and the diffusion coefficient for glucose.