Cationic surfactant as a sensitizer for the spectrophotometric determination of sulphur dioxide in air and evaluation of a new absorbing solution for fixing sulphur dioxide

A simple extractive spectrophotometric method for the determination of trace amounts of sulphur dioxide in ambient air after fixing the gas in triethanolamine (TEA)-mannitol solution is developed. The proposed trapping solution permits higher flow rates for sampling atmospheric sulphur dioxide and the fixed SO2 has prolonged stability. The reaction of iodate with sulphur dioxide in the presence of an acid and excess chloride ions leads to the formation of ICl2- species. The formed species is used to iodinate dichlorofluorescein to form dichlorodiiodofluorescein and it is extracted into isoamyl alcohol. The iodinated compound is sensitised with a cationic surfactant, cetrimide, in the presence of acetate-acetic acid buffer (pH 5.9 ± 0.1) to enhance the sensitivity of the method. The method obeys Beer's law in the concentration range 0-8 μg of sulphur dioxide. The relative standard deviation is 3.6% for ten determinations at 6 μg of sulphur dioxide. The effect of interfering gases on the determination will be discussed. The method has been applied for the determination of sulphur dioxide in the vicinity of a sulphuric acid plant and the results obtained were compared with the widely used West and Gaeke method. The method can be used to determine a concentration as low as 0.5 μg of sulphur dioxide. © Elsevier.