Automatic determination of ascorbic acid by flame atomic absorption spectrometry

Abstract

A continuous flow procedure is proposed for the indirect determination of ascorbic acid based on its reducing properties. Chromium(VI) in acid medium was injected into a ascorbic acid stream, and the Cr(VI) was reduced to Cr(III). This Cr(III) formed was retained on-line, proportionally to the ascorbic acid concentration in the sample, on a poly(aminophosphonic acid) chelating resin, which is only selective for this oxidation state, while non-reduced Cr(VI) was determined by flame atomic absorption spectrometry. The proposed method allows the determination of ascorbic acid in the range 0.4–20 μg ml −1 with a relative standard deviation of 2.0% at a rate of ca. 90 samples per hour. This method has been applied to the determination of ascorbic acid in pharmaceutical preparations and fruit juices.