Determination of sulfur dioxide and ascorbic acid in beverages using a dual channel flow injection electrochemical detection system

Abstract

A new flow injection method is described for the simultaneous determination of ascorbic acid (AA) and sulfur dioxide in red and white wines and various fruit juices. The flow injection manifold consists of a dual channel amperometric detection system, where AA is detected at a glassy carbon electrode set at +0.42 V (versus Ag/AgCl) and sulfur dioxide is detected at a platinum electrode at +0.90 V (versus Ag/AgCl) after separation by a gas diffusion unit. In the application of this method to the analysis of both analytes in wines and fruit juices, the results for white wines, fruit juices and juice concentrates agree well with data obtained by ion-exclusion chromatography. However, in the case of red wines and a sweet white wine, it is necessary to extract the analytes using solid phase extraction on a quaternary amine SAX cartridge before acceptable results are achieved by the new flow injection method. The linear dynamic range for AA is 3–50 mg/l with a detection limit of 1.5 mg/l and for sulfur dioxide the linear range is 0.25–15 mg/l with a detection limit of 0.05 mg/l. The sampling frequency for both analytes is 30/h.