Reverse-FIA with spectrophotometric detection method for determination of vitamin C

Abstract

Simple reverse flow injection analysis (rFIA) manifold with spectrophotometric detection was developed for an indirect determination of ascorbic acid. Parameters such as stability, accuracy and precision were established for the method and evaluated statistically to assess the applications of the method. Ascorbic acid in this procedure accelerates dediazoniation reaction of formed diazonium ions; hence its quantity can be determined by monitoring the derivatization product from coupling unreacted diazonium ion with phenol to give an azo dye (coupling reaction). The rFIA design was based on the injection of sodium nitrite into an acidic p-aminoacetophenon carrier stream in which diazonium ion was formed. This ion was inhibited by ascorbic acid stream before coupling with the phenol-Na₂CO₃ stream. Under optimum conditions, ascorbic acid acts in accordance with the Beer’s law at two concentration ranges 0.4–6.5 μg ml⁻¹ (R = 0.9995) and 7.0–20.0 μg ml⁻¹ (R = 0.9949), with detection limits of 0.25 μg ml⁻¹. The developed method was applied to the determination of vitamin C in pharmaceutical formulations which produced satisfactory results compared with the standard methods reported in the British Pharmacopoeia.