Direct determination of free sulfur dioxide in wine and dried apple samples by using a gas generating and purging device coupled to a continuous flow (injection) system

Abstract

Two new approaches for the direct determination of free sulfur dioxide in wine and dried apple samples are proposed. Both use flow injection manifolds including a dynamic gas-extraction device to generate and purge gaseous SO₂ species from an acidified sample solution. One of the methods involves in situ concentration and continuous monitoring of the reaction product (p-rosaniline reaction system). The kinetic features of the absorbance–time profiles obtained in real time are used for quantification. The other method uses a flow-reversal manifold to directly process the gaseous plug generated from the sample; it provides multipeak recordings on which the SO₂ determination is based. The proposed methods allow SO₂ to be quantified over the ranges 0.03–3 and 0.75–75 µg ml^–1, respectively. Both were applied to the direct determination of SO₂ in liquid and solid food samples (wine and dried apple were taken as models of real samples) with relative standard deviations of 5–6% and sampling frequencies of 10–12 h^–1.