US EPA

1238176 

Journal Article 

Spectrophotometric Determination of Sulphur Dioxide 

Parashar, DC; Raman, V; Singh, M 

1987 

Yes 

Environmental Pollution
ISSN: 0269-7491
EISSN: 1873-6424 

NIOSH/00174639 

45 

2 

125-132 

A method for the determination of sulfur-dioxide (7446095) (SO2) in air using the reduction of hexavalent chromium by SO2 trapped in aqueous morpholine was reported. SO2 gas generated by the reaction of hydrochloric-acid and sodium-sulfite was collected in a gas sampler and diluted with air to a concentration of 20 micrograms per milliliter. The SO2 gas was injected into a series of Corning gas samplers in volumes of 1, 2, 3, 4, and 5 milliliters. The samplers were flushed with nitrogen through a series of micro impingers containing 0.4 percent morpholine solution, and the amount of SO2 absorbed in the impingers was determined. The trapped SO2 was exposed to potassium-chromate, reducing the hexavalent chromium to trivalent chromium. Reaction of the remaining hexavalent compound with diphenylcarbazide yielded a soluble red violet complex with an absorption maximum at 540 nanometers. Water served as the control. The decrease in the absorbance values of the red violet complex were proportional to the amount of SO2 present in the samples for concentrations between 0.4 and 4.0 micrograms per milliliter. Nitrite ion was found to interfere with the method, and this could be prevented by adding a separate trap containing 0.6 percent sulfamic-acid prior to the micro impinger with the absorbing solution. Sulfide ion was also found to interfere, and the authors recommend checking the level of this contaminant when using this method. Application of the method to the analysis of SO2 in the air in a chemical laboratory was described. 

DCN-162422; Chemical manufacturing industry; Air contamination; Analytical methods; Sulfur compounds; Analytical chemistry; Trace analysis; Colorimetry; Sulfur oxides