Determination of Ascorbic Acid in Long Life Juices by Cyclic Voltammetry Using External Standards and Standard Addition Methods: An Experimental Proposal for Teaching Analytical Instrumental Chemistry

Ascorbic acid (vitamin C) is essential to our body and can be found in leafy vegetables, legumes and fruits, as well as in natural and industrialized juices. The concentration of vitamin C present in long life juices is normally informed by the manufacturer on the package label. The objective of this work was to use an electroanalytical technique, cyclic voltammetry, to determine the concentration of vitamin C in long-life juices. From the dilution of a 100 mmol L -1 stock solution of ascorbic acid, the calibration curves were prepared by the method of external standards or of standard addition. Cyclic voltammograms (CVs) were recorded from 0 to +1.0 V, with v = 50 mV s -1 . The solutions were prepared in the presence of KCl 0.34 mol L -1 as supporting electrolyte, including the samples. Measurements were taken in triplicate. It was found that vitamin C is present in all juice brands analyzed, and in some cases in a concentration very different from the value informed on the package label by the manufacturer. The present work showed the viability of using the CV technique for the determination of vitamin C in a food product, which is relevant for the teaching of electrochemistry.