The use of isopropanol to distinguish H2SO4 from particulate sulfate on filters

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Abstract
Potential interferences in the anhydrous isopropanol (a‐IPA) extraction method for separating sulfuric acid from particulate sulfate on filters were investigated. The method involves separation and recovery of the acid with a‐IPA, followed by aqueous extraction of the particulate sulfate. Analysis for sulfate in the two separate fractions was performed by ion chromatography. The solubility of ammonium sulfate in a‐IPA was measured and the effects of temperature and moisture content of the solvent on ammonium sulfate solubility were determined. The solvent recovery procedure was used to analyze samples collected at an oil‐fired utility boiler. Before analysis, each filter was cut in half and one half of each filter was exposed to an ammonia atmosphere to neutralize any free sulfuric acid. All filter halves were then extracted with a‐IPA followed by a separate aqueous extraction by ultrasonication. Neither a small uptake of moisture by the a‐IPA nor elevated temperatures up to 30° C had a significant effect on the solubility of ammonium sulfate in IPA. Ammonium sulfate was determined to be very highly insoluble in a‐IPA and therefore, exposure of samples to any source of ammonia will result in low recoveries of sulfuric acid by the solvent recovery procedure.