Determination of sulphite in wines by gas-diffusion flow injection analysis utilizing spectrophotometric pH-detection

A photometric flow injection analysis (FIA) method, using a gas-diffusion cell, has been developed for the determination of sulphite in wines. The method is based on the change of the absorbance of an indicator solution when sulphur dioxide, liberated from the matrix, diffuses via a permeable membrane into the indicator solution and locally shifts the pH. As indicator, bromocresol green was used. The method is applicable in the range of 1-20 mg/l sulphite and the lower limits of detection is 0.1 mg/l. The reproducibility of the analysis for wines are in the range of 0.7-1.5%. Addition of 10% (v/v) ethanol to all solutions and extensively flushing off these solutions with nitrogen before use is crucial to obtain reliable results. The flushing with nitrogen may be considered as a disadvantage of the present method. The method is applicable to red, white and rose wines. Carbon dioxide interferes the measurement and therefore the method cannot be used for sparkling wines and beers. The results obtained with the FIA method agrees well with the iodometric titration method using biamperometric detection.