Development of method for the analysis of sulfur dioxide in ambient air

Abstract

In this study, investigation of sulfur dioxide absorbing reagents instead of Tetrachloromecurate solution (TCM) such as 0.01 N NaOH, 2% glycerol in 0.05 N NaOH and buffered formaldehyde solution were performed. Buffered formaldehyde solution was found to be efficient absorbing reagent for analysis of sulfur dioxide. Buffered formaldehyde solution absorbed sulfur dioxide to form hydroxymethane sulfonic acid which liberated sulfite by reaction with base. The sulfite was analysed by many methods such as iodine method, alkalimetric method and aniline method. Aniline method provided better accuracy, precision and sensitivity than the others. Thus, aniline method was selected for analysis of SO₂ in air. By this aniline method, concentration of sulfur dioxide found provided positive deviation of 5% from standard sulfur dioxide in inert gas (oxygen free nitrogen gas) and sulfur dioxide in ambient air could be determined from 25 µg/m³. Comparison to pararosaniline method which gave negative deviation of 3% from standard sulfur dioxide in inert air, this aniline method resulted in lower accuracy and sensitivity but insignificant difference for high sulfur dioxide concentration. In addition the chemicals used are cheaper and easily find.