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 (n_app) and the corresponding values of heterogeneous rate constants (k_app) 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 n_app (and k_app) 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 k_app values at the alloy electrode. Furthermore, the larger k_app 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 k_app value and the diffusion coefficient for glucose.