Determination of ascorbic acid by perturbation of the oscillation pattern of the Belousov-Zhabotinskii reaction using a continuous flow system

Abstract

It is proposed the potentiometric determination of ascorbic acid (vitamin C) in medicines, in a flow system, using as principle the effect of this substance in the oscillation pattern of the Belousov-Zhabotinskii reaction. This reaction involves the oxidation of an organic compound, such as malonic acid, by bromate ions in sulfuric acid medium, with the cerium (IV) ion used as a catalyst. Both frequency and amplitude of oscillations can be used as analytical parameters. Ascorbic acid can reduce the potential difference, increasing the amplitude of the Belousov-Zhabotinskii reaction when this substance is injected into the reaction medium. The chemical system is disturbed with varying amounts of ascorbic acid, which results in an increase in amplitude that is linearly proportional to the concentration of ascorbic acid. Most ions commonly found in drug samples do not interfere with the determination. The experimental conditions were chosen through a 2⁴ factorial design, where the concentrations of the reagents potassium bromate, cerium (IV) sulphate, malonic acid and sulfuric acid were the studied variables. The methodology for the determination of ascorbic acid resulted in a relatively simple procedure, with a detection limit of 1.63 x 10^-4 mol L^-1. In the determination of ascorbic acid in drug samples, results were obtained in accordance with the values ??declared by the manufacturers. The developed method presents itself as an alternative for the determination of ascorbic acid in medications, as the procedure is relatively simple and inexpensive.