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.