Chemical amplification method for the determination of atmospheric sulphur dioxide

Abstract

A sensitive spectrophotometric method is described for the determination of trace levels of sulphur dioxide in ambient air after fixing the gas in triethanolamine (TEA) or triethanolaminemannitol absorbing solutions. The method is based on the reaction of sulphur dioxide with iodine to form iodide and after the extraction of unreacted iodine, the iodide was oxidized to iodate by bromine. The generated iodate is utilized to oxidize hydroxylamine to nitrite which produces an azo dye in the presence of p-nitroaniline and N-(l-naphthyl)ethylenediamine dihydrochloride (NEDA) in acid medium with maximum absorption at 545 nm. The system obeys Beer's law over the concentration range 0-5 μg of sulphur dioxide in a final volume of 25 ml. The relative standard deviation is 2.5% at 4 μg of sulphur dioxide (n = 10). The interference of other gaseous species were suitably overcome by the proper reaction conditions. The developed method was applied to determine low levels of sulphur dioxide generated using permeation devices and ambient levels of sulphur dioxide in the vicinity of a sulphuric acid plant.