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

Abstract
Flow injection analysis (FIA) methods for the spectrophotometric determination of CO₂ and SO₂ in wines are described. The determination of CO₂ 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 SO₂ is based on the decoloration of malachite green by sulphur dioxide. Two FIA manifolds are presented; one for the determination of CO₂ in sparkling wines and another for the simultaneous determination of CO₂ and SO₂ 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 CO₂, recovery values between 93.5 % and 111 % were found. RSD lower than 4.5 % for SO₂ and 2.4 % for the CO₂ determination were found. The sampling rates achieved were: 30 h^-1 for the uniparametric system and 40 h^-1 for the biparametric system. The single determination manifold is applicable in the concentration ranges of 0.5 to 4 g L^-1 of CO₂, and the simultaneous determination manifold in the range of 0.25 to 3 g L^-1 of CO₂ and 0.05 to 0.3 g L^-1 of SO₂.