Simultaneous voltammetric determination of ascorbic acid and uric acid using a seven-hole carbon nanotube paste multielectrode array

In this study, a seven-hole multielectrode array comprising six carbon nanotube paste working electrodes and a carbon nanotube paste counter electrode (Fig. 1) was designed and fabricated. To reduce sample consumption, a novel 'micro-drop' cell including an Ag/AgCl micro-reference electrode was fabricated for simultaneous determination of ascorbic acid and uric acid via cyclic voltammetry (CV) and square wave voltammetry (SWV) on the multielectrode array fabricated. In the simultaneous detection of ascorbic acid and uric acid using CV at carbon nanotube paste working electrodes, the oxidation peak separation of ascorbic acid and uric acid increased from 0.09 V to 0.15 V, and the oxidation peak currents of ascorbic acid and uric acid were greatly enhanced compared with carbon paste working electrodes. Under the optimized conditions, the oxidation peak currents were linear over ranges from 2.0 × 10^-6M to 8.0 × 10^-4M for ascorbic acid in the presence of 6.0 × 10^-6M uric acid, and from 2.0 × 10^-7M to 8.0 × 10^-5M for uric acid in the presence of 2.0 × 10^-4M ascorbic acid with detection limits of 1.0 × 10^-6M and 9.0 × 10^-8M (S/N = 3), respectively. The effect of potential interferences including compounds usually found in human fluids (l-lysine, glucose, citric acid, glycin and cystine) were examined. The proposed method has been successfully applied to the determination of ascorbic acid and uric acid in human urine with satisfactory results. This work demonstrates that the use of carbon nanotube paste multielectrode array is a promising strategy for simultaneous electrochemical determination of isomers of organic compounds.