Determination of ascorbic acid in a mixture of ascorbic acid and uric acid at a chemically modified electrode

The electrochemical behavior of ascorbic acid (AA) at a 3,4-dihydroxybenzaldehyde (DHB) modified glassy carbon electrode has been examined by voltammetry and amperometry. The results indicated that the modified electrode reduces the overpotential of AA oxidation, while the oxidation process of uric acid (UA) is little affected. The anodic peak due to the oxidation of AA was pH dependent and occurred at 0.15 V (vs. SCE) at pH 7.4, which is at least 250 mV more negative than that at a bare glassy carbon electrode. Rotating disk electrode experiments revealed that the oxidation current is solely controlled by mass-transport process in solution. AA was detected amperometrically in a flow injection system at the modified electrode with excellent sensitivity. Calibration curves were linear over the concentration range of 0.7 mu M to 1.0 mM with a pH 7.4 phosphate buffer solution as the carrier. The detection limit was 0.30 mu M. Selectivity was illustrated by the analysis of ascorbic acid in the presence of uric acid. The modified electrode also shows good anti-fouling properties towards surface active materials.