Flow-Injection Amperometric Determination of Ascorbic Acid Using a Graphite-Epoxy Composite Electrode Modified with Cobalt Phthalocyanine

A flow injection method is reported for the determination of ascorbic acid based on amperometric detection, using a cobalt(II) phthalocyanine (CoPc) modified graphite-epoxy electrode. The amperometric respons was evaluated with regard to pH, ionic strength of the electrolyte, flow rate of the carrier solution, injected sample volume and conditioning time of the electrode. The limit of detection was 0.013 mM (50 mL injected), and the calibration plot was linear in the ranges of 0.025-1.0 mM (correlation coefficient, r=0.9989, n=6) and 1.0-10 mM (r=0.9997, n=5). The relative standard deviation for the measurement of ascorbic acid at several concentrations was £1%. The modified electrode was found to retain its full response in flowing streams for several days of operating time. The results of ascorbic acid quantification in fruit juices and vitamin tables are reported.