A method for the determination of sulfuric acid in the atmosphere by ion chromatography was investigated. Sulfuric acid in aerosols collected on a Teflon filter was extracted with benzaldehyde as a selective solvent for sulfuric acid, and then sulfuric acid in benzaldehyde was counterextracted with distilled water for ion chromatography. In the counterextraction, a portion of benzaldehyde dissolved in distilled water, and was rapidly oxidized to benzoic acid. The benzoic acid produced by oxidation of benzaldehyde seriously interfered with the determination of sulfuric acid by ion chromatography due to the overlapping peaks. Various methods such as the reduction with zinc powder, the extraction with benzene, and the cooling were tested for removal of benzoic acid. However, no sufficient removal by these methods was obtained. Instead of these methods, sulfuric and benzoic acids were separated by exclusion ion chromatography. Sulfuric acid was separated from benzoic acid by using ion exclusion column, and then the portion including sulfuric acid was reinjected to an ion chromatograph installed with the anion separator column for determination of sulfuric acid. The concentrations of sulfuric acid in the atmosphere at Hiyoshi, Yokohama from January to October, 1985 were 0.13~0.95 μg/m3. The detection limit of sulfuric acid by this method was 0.005 μg/m3 at sampling 4 m3 of air.
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