An Automatic Spectrophotometric Titration Procedure for Ascorbic Acid Determination in Fruit Juices and Soft Drinks Based on Volumetric Fraction Variation

Abstract

A spectrophotometric flow titration procedure for ascorbic acid in fruit juices and soft drinks based on volumetric fraction variation employing a reaction with 2,6-dichloroindophenol is described. A flow network was designed to implement the multicommutation process and a set of microcomputer controlled three-way solenoid valves was employed to handle the insertion of the titrand and titrant solutions into the analytical path. All the steps involved in the titration procedure were carried out automatically without any operator assistance. Fruit juices and soft drinks could be analyzed without any prior chemical treatment. Accuracy was assessed by comparing results with those obtained by the reference method (AOAC). No significant differences at 95% confidence level were observed. Other profitable features were achieved such as a percentual standard deviation of results of 1.1% (n = 5) for a typical juice sample containing 1.2 mmol L^–1 ascorbic acid, a low sample consumption (6 μL per run), and an analytical throughput ranging from 5 to 30 determinations per hour for sample concentrations ranging from 0.6 to 6.0 mmol L^–1.