Voltammetric determination of ascorbic acid with zinc oxide modified glassy carbon electrode

Zinc oxide (ZnO) nanostructures electrodeposited from aqueous zinc nitrate solution at 70 degrees C onto glassy carbon electrode (GCE) were used as electrochemical detectors. The morphology, structure, chemical composition and conductivity of the as-deposited layers were determined using scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray analysis and UV-Vis spectroscopy. A highly oriented crystalline ZnO deposit made of a dense array of randomly oriented hexagonal nanorods was obtained without any additives in solution. The electrocatalytic oxidation of ascorbic acid (AA) was studied using cyclic voltammetry in 0.1 M phosphate buffer solution at pH 6.8. Comparing the response for AA oxidation on the bare and modified electrodes, the peak potential was shifted to -0.45 V on ZnO/GCE with higher current densities and transfer coefficient, due to a simultaneous increase in oxidation rate and surface area. A linear relationship was determined between the anodic peak current and the AA concentration in the range of 0.1-5 mM.