Electrocatalytic response of carbohydrates at copper-alloy electrodes

The voltammetric responses observed for carbohydrates and polyalcohols at s imilar to 0.60 V in 0.10 M NaOH are significantly larger at preanodized CuM n (95:5) electrodes as compared to preanodized pure Cu electrodes. Apparent values for the number of electrons transferred (n(app)) and the correspond ing values of heterogeneous rate constants (k(app)) are estimated for selec ted reactants from the slopes and intercepts, respectively, of Koutecky-Lev ich plots of background-corrected voltammetric currents obtained at CuMn an d Cu rotated disk electrodes (RDEs). Values of n(app) (and k(app)) for sorb itol and glucose are 11.8 (9.2 x 10(-3) cm s(-1)) and 11.7 (8.0 x 10(-3) cm s(-1)), respectively, at a CuMn RDE. These are compared to the values 10.4 (1.8 x 10(-3) cm s(-1)) and 9.6 (2.0 x 10(-3) cm s(-1)) for sorbitol and g lucose, 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 re sult of larger k(app) values at the alloy electrode. Furthermore, the large r 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 sen sitivities of the k(app) value and the diffusion coefficient for glucose. ( C) 2001 Elsevier Science B.V. All rights reserved.