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

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 p urge gaseous SO2 species from an acidified sample solution. One of the methods involves in situ concentration and continuous monitoring of t he reaction product (p-rosaniline reaction system). The kinetic featur es of the absorbance-time profiles obtained in real time are used for quantification. The other method uses a flow-reversal manifold to dire ctly process the gaseous plug generated from the sample; it provides m ultipeak recordings on which the SO2 determination is based. The propo sed methods allow SO2 to be quantified over the ranges 0.03-3 and 0.75 -75 mu g ml(-1), respectively. Both were applied to the direct determi nation of SO2 in liquid and solid food samples (wine and dried apple w ere taken as models of real samples) with relative standard deviations of 5-6% and sampling frequencies of 10-12 h(-1).