CHEMICAL AMPLIFICATION METHOD FOR THE DETERMINATION OF ATMOSPHERIC SULFUR-DIOXIDE

A sensitive spectrophotometric method is described for the determinati on of trace levels of sulphur dioxide in ambient air after fixing the gas in triethanolamine (TEA) or triethanolaminemannitol absorbing solu tions. The method is based on the reaction of sulphur dioxide with iod ine to form iodide and after the extraction of unreacted iodine, the i odide was oxidized to iodate by bromine. The generated iodate is utili zed to oxidize hydroxylamine to nitrite which produces an azo dye in t he presence of p-nitroaniline and N-(l-naphthyl)ethylenediamine dihydr ochloride (NEDA) in acid medium with maximum absorption at 545 nm. The system obeys Beer's law over the concentration range 0-5 mu g of sulp hur dioxide in a final volume of 25 mi. The relative standard deviatio n is 2.5% at 4 mu g of sulphur dioxide (n = 10). The interference of o ther gaseous species were suitably overcome by the proper reaction con ditions. The developed method was applied to determine low levels of s ulphur dioxide generated using permeation devices and ambient levels o f sulphur dioxide in the vicinity of a sulphuric acid plant.