Voltammetric determination of ascorbic acid by use of a carbon paste electrode

Abstract

It has been shown that the oxidation of ascorbic acid at a carbon paste electrode is similar to that at a platinum electrode. The half-peak potential is somewhat higher than the half-wave potential at a dropping-mercury electrode. The peak current is proportional to the concentration of ascorbic acid in the range 10^–6–10^–3M and the reproducibility is better than ±1 per cent. Chloride and sulphur compounds, such as sulphides and thiols, do not interfere, and sulphite can be determined at the same time as the ascorbic acid. Some substituted phenols interfere but can often be detected by reversing the direction of polarisation. Reductones interfere but tin(II) and manganese(II) do not. A method has also been developed to determine ascorbic acid in the presence of an excess of iron. Different extraction media are discussed in terms of their influence on the redox potential of iron.

Comparative titrimetric determinations of ascorbic acid in some fruits, vegetables and beverages gave higher results than the voltammetric method.