[Catalytic kinetic spectrophotometric determination of trace ascorbic acid].

In this paper, a new catalytic kinetic spectrophotometric method for the determination of trace amounts of ascorbic acid has been studied. The method is based on the activation effect of ascorbic acid on vanadium (V) catalyzed oxidation of deoxidized rhodamine B by potassium bromate in weak acidic medium at pH 4.5. The optimal experimental conditions have been discussed. The absorbance was measured at 555 nm. The linear range of the method was 0-7.0 microg x mL(-1). The detection limit for ascorbic acid was 2.5 x 10(-7) g x L(-1). The method has been applied to the determination of ascorbic acid in vitamin C tablet and tomato with satisfactory results.