Determination of S(IV) in particulate matter

The presence of sulfite and other S(IV) species in power plant fly ash and other particulate matter released to the environment is of interest because of the potential health-related biological activity of sulfite anions if these particles are inhaled. A method was developed for extracting S(IV) from particle samples with a formaldehyde-based solution containing a chelating agent for the improved dissolution of insoluble sulfites. Measurements were made subsequently using a spectrophotometric determination based upon the Schiff reaction with paraosaniline. Although no detectable sulfites species were found in older samples of power plant coal fly ash, about 10 ppM was found in fresh coal fly ash from a small power unit and about 13 ppM was found in a coal-oil mixture fly ash. Larger quantities (up to 1600 ppM) were found in lead and copper smelter flue dust samples