Description
This method describes the quantitative determination of sulphite in foods. The method has been tested for the determination of sulphite added as a preservative to juices, wines and vinegar, dried fruit, peeled potatoes and minced meat in the concentration range 0.03 – 0.60 g SO2/kg. The limit of detection is 0.01 g/kg. The sample is distilled from acid solution in a semimicro Kjeldahl apparatus. The SO2 formed evaporates and reacts in the receiver with 5,5’ –dithiobis (2- nitrobenzoic acid) to form the intensely yellow 5- mercapto-2-nitrobenzoic acid. The intensity of the colour is read spectrophotometrically. The concentration of the standard solution is determined by iodometric titration.