A selective catalytic voltammetric determination of vitamin C in pharmaceutical preparations and complex matrices of fresh fruit juices

A simple, selective and precise voltammetric method for the determination of ascorbic acid in pharmaceutical preparations and fresh fruit juices-complex matrices containing various reducing compounds-is described. The method is based on the electrocatalytic oxidation of ascorbic acid in homogeneous solution using electrogenerated ferriciniumcarboxylic acid as mediator. The pH and mediator concentration affecting the performance of the electrocatalytic oxidation of the analyte were optimized. The method was applied to determine vitamin C in deeply coloured, viscous and turbid fruit juice samples with ascorbic acid contents ranging from 15-45 mg per 100 ml, without further dilution, concentration or other pre-treatment of the samples. The amount of mediator used varied depending on the ascorbic acid concentration in the samples. The method was also used for pharmaceutical analysis using a calibration graph. For fruit juice samples the standard addition technique was adopted to prevent the matrix affecting the accuracy of the determination. The relative standard deviation for the analysis of vitamin C in fruit juices ranged from 1.5-5%. The reliability of the method was established by parallel determination against the official methods.