Spectrophotometric determination of carbon dioxide and sulphur dioxide in wines by flow injection

Abstract

Flow injection analysis (FIA) methods for the spectrophotometric determination of CO 2 and SO 2 in wines are described. The determination of CO 2 is based on the colour change of a low capacity buffer (containing an acid-base indicator) due to the dissolved carbon dioxide. The determination of SO 2 is based on the decoloration of malachite green by sulphur dioxide. Two FIA manifolds are presented; one for the determination of CO 2 in sparkling wines and another for the simultaneous determination of CO 2 and SO 2 in table wines. The analytes are isolated inside the manifold from the sample matrix using gas-diffusion units. Regression equations (FIA versus reference methods) showed no statistical difference, at 95 % confidence level, between the two sets of results for both determinations; additionally, for the determination of CO 2 , recovery values between 93.5 % and 111 % were found. RSD lower than 4.5 % for SO 2 and 2.4 % for the CO 2 determination were found. The sampling rates achieved were: 30 h -1 for the uniparametric system and 40 h -1 for the hiparametric system. The single determination manifold is applicable in the concentration ranges of 0.5 to 4 g L -1 of CO 2 , and the simultaneous determination manifold in the range of 0.25 to 3 g L -1 of CO 2 and 0.05 to 0.3 g L -1 of SO 2 .