Flow electrochemical determination of ascorbic acid in real samples using a glassy carbon electrode modified with a cellulose acetate film bearing 2,6-dichlorophenolindophenol

An ascorbate sensor based on a glassy carbon electrode modified with a cellulose acetate polymeric film bearing 2,6-dichlorophenolindophenol (CA/DCPI-CME) was constructed. The overall reaction obeys a catalytic regeneration mechanism (EC mechanism) and the electrochemical rate constant kf for the electrocatalytic oxidation of ascorbic acid was evaluated. The modified electrodes were mounted in a flow injection (FI) manifold, poised at +100 mV versus Ag/AgCl/3 M KCl at pH 6.5 and utilized for the determination of ascorbic acid in beverages and pharmaceuticals. Good correlation with a reference method was attained. Interferents of various molecular sizes were tested. Calibration graphs were linear over the range 0.02-1 and 0.1-6 mM ascorbic acid for CA/DCPI sensors hydrolyzed in KOH and ZnCl2 solution, respectively. The throughput was 25 samples per hour and the CV was for a 0.4 mM ascorbic acid solution 0.75 (n=14) and 1.2% (n=10) for CA/DCPI sensors hydrolyzed in KOH and ZnCl2 solution, respectively. The recovery was 92-110%. The sensors showed very good repeatability and operational stability. (C) 2000 Elsevier Science B.V. All rights reserved.