Application of square-wave voltammetry for the determination of ascorbic acid in soft drinks and fruit juices using a flow-injection system

Abstract

The application of square-wave voltammetry for detection in the flow-injection determination of ascorbic acid in soft drinks and fruit juices was investigated. The pH of the solution was buffered at 2.87 to stabilize the ascorbic acid prior to analysis. Parameters such as scan rate, square-wave amplitude, step height and flow-rate of electrolyte were found to have little effect on the potential, but a significant effect on the current. The analytical current is only slightly affected by the flow-rate of the electrolyte and a maximum scan rate of 0.5 V s-1 can be used. As a compromise between sensitivity and selectivity, 40 mV was chosen as the amplitude of the square wave and 10 mV as the potential step height. Similarly, a flow-rate of 0.5 ml min-1 and an injection volume of 100 μl were chosen as a compromise between the sensitivity and resolution of the FIA method. Using the above procedures, the maximum number of samples that could be analysed was 120 h-1. The linear calibration range was from 2 x 10-6 to 6 x 10-3 M and the determination limit (10δ) was 2 x 10-7 M. No significant interference was found from additives commonly found in juices and drinks samples within their normal concentration ranges. Four juice samples were analysed using the developed method and the results were compared with those given by the established AOAC method. No significant difference was observed between the two methods used for the four samples studied.