Method for the sampling and analysis of sulphur dioxide

A sensitive spectrophotometric method for the determination of SO₂ after fixing in a new trapping solution of NaOH-citrate is described. The method is based on the redox reaction of SO₂ with bromate in acid medium to liberate bromine which brominates 2,7-dichlorofluorescein (DCF) and subsequent measurement of the brominated product at 535 nm in an organic phase. Absorption characteristics of the developed trapping solution and application studies are also described. The relative standard deviation was 3.8% (10 g SO₂). Interferences by NO₂ and H₂S were eliminated.