Continuous flow molecular emission cavity analysis of sulphite and sulphur dioxide

Abstract

A continuous flow method for the determination of sulphite (1–50 µg ml^–1) by molecular emission cavity analysis is described. The sample is mixed with an excess of orthophosphoric acid in a flow system and the sulphur dioxide evolved is continuously transferred into the cavity for generation of the S₂ molecular emission. The analysis is completely automated, requires no sample pre-treatment and samples can be analysed at a rate of 24 per hour with a relative error of 1–2%. Various anions and cations interfere and attempts have been made to eliminate their effect on the final measurement. The results obtained by the proposed procedure compare well with the expected values when the method was applied to soft drinks, wines and air samples.