Square-Wave Voltammetric Determination of Ascorbic Acid Based on its Electrocatalytic Oxidation at Zeolite-Modified Carbon-Paste Electrodes

Carbon-paste electrodes modified with Fe(III)-Y zeolite have been used to study the electrocatalytic oxidation of ascorbic acid. The ion-exchange behavior of the modified electrodes in different supporting electrolytes was investigated. Maximum cathodic current due to reduction of the exchanged Fe(III) ions was observed in phosphate buffer, pH 5. The modified electrode acts as a catalyst for electrooxidation of ascorbic acid, lowering the overpotential of the reaction by ~200 mV. The faster rate of electron transfer results in a great enhancement of the cathodic peak current compared to those observed for the unmodified electrode. The effect of several parameters such as pH and concentration of the supporting electrolyte was investigated. The square-wave voltammetric response of the electrode to ascorbic acid is linear in the range 4.0×10-7 to 1.2×10-3 M with a detection limit of 2×10-8 M. The interfering effect of several cationic species and organic compounds was investigated and tolerance limits were obtained. The method was applied to the determination of ascorbic acid in citrus fruits.