Determination of L-ascorbic acid in fruit and vegetable juices by flow injection with immobilised ascorbate oxidase

Abstract

Ascorbate oxidase was immobilised on cyanogen bromide activated-Sepharose 4B and incorporated in a flow-injection system with amperometric detection at a glassy carbon electrode at +0.6 V. On passage through the immobilised ascorbate oxidase a fraction of the L-ascorbic acid was converted into dehydroascorbic acid and the decrease in signal was measured. This could be directly related to the amount of L-ascorbic acid present. The calibration graph was linear over the range 0–400 ng ml^–1 with a correlation coefficient of 0.9994. The detection limit (2σ) in phosphate buffer (0.08 M, pH 5.5) was 4.0 ng ml^–1. The relative standard deviation for a 200 ng ml^–1 standard was 1.0%(n= 10) and the sampling throughput was 30 samples h^–1. The method was used for the simple and rapid determination of L-ascorbic acid in fruit and vegetable juice.