Selective spectrophotometric method for the determination of ascorbic acid in pharmaceutical preparations and fresh fruit juices

Abstract

A simple and selective method for the determination of ascorbic acid in pharmaceutical preparations and fresh fruit juices is described. The procedure is based on the reaction of ascorbic acid with the zinc chloride salt of diazotized 1-aminoanthraquinone (Fast Red AL salt) in an acidic medium, followed by development of a blue colour (λ_max 630 nm) in alkaline solution. Different variables affecting the colour development were studied and optimized. The method was used to determine between 5 and 25 µg ml^–1 of ascorbic acid in the final measured solution. The simplicity of the method permits rapid analysis, suitable for routine control. The method is highly specific for the determination of ascorbic acid in the presence of dehydroascorbic acid and all other vitamins normally encountered with it in pharmaceutical dosage forms. Moreover, the proposed method can also be applied to the determination of ascorbic acid in some fresh fruit juices without interference from coloured and other substances present in the fruit extracts. The reliability of the method was established by parallel determinations against the official British pharmacopoeial method.