DETERMINATION OF TOTAL SULFUR-DIOXIDE IN BEER BY FLOW-INJECTION SPECTROPHOTOMETRY USING GAS-DIFFUSION AND THE MERGING ZONES TECHNIQUE

A flow injection system for the determination of total sulphur dioxide in beer is described. The methodology involves the same colorimetric reaction of the reference method between SO2, p-rosaniline and formald ehyde. The sample is introduced into the manifold without previous pre treatment, the hydrolysis process, isolation of the SO2 from the matri x and the colorimetric reaction, being carried out inside the flow tub es. To isolate the SO2, a gas-diffusion unit was included in the syste m and to minimise p-rosaniline consumption, a merging zones technique was used. The results obtained were in good agreement with a reference method (relative deviations lower than 5%), the precision being bette r than 2.5% (relative standard deviation). A sampling-rate of 30 sampl es per hour was obtained and the consumption of p-rosaniline was reduc ed 10 fold when compared to the reference method.