Monitoring of vitamin C species in aqueous solution by flow injection analysis coupled with an on-line separation with reversed-phase column

Two vitamin C species of ascorbic acid and dehydroascorbic acid in aqueous solution were monitored by flow injection analysis. Ascorbic acid and dehydroascorbic acid were resolved by a reversed-phase column, and dehydroascorbic acid was reduced to ascorbic acid by an on-line post-column reaction with dithiothreitol. Both natural and reduced ascorbic acids were photometrically detected at 260 nm, and the two vitamin C species were simultaneously determined. The determination range was from 0 to 8 × 10⁻⁵ M with a limit of detection of 1.7 × 10⁻⁶ M. The proposed method was applied to the conversion monitoring of ascorbic acid and dehydroascorbic acid in weakly acidic to weakly alkaline aqueous solutions, as well as to the determination of the vitamin C in some beverage samples.