Determination of total sulphur 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 formaldehyde. The sample is introduced into the manifold without previous pretreatment, the hydrolysis process, isolation of the SO2 from the matrix and the colorimetric reaction, being carried out inside the flow tubes. To isolate the SO2, a gas-diffusion unit was included in the system 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 better than 2.5% (relative standard deviation). A sampling-rate of 30 samples per hour was obtained and the consumption of p-rosaniline was reduced 10 fold when compared to the reference method