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RECEIVED for review April 18, 1980. Accepted .June 16, 1980. This research was supported in part by NASA grant NSG03-001-001. This work was presented at the 22nd Rocky Mountain Conference of the Rocky Mountain Chromatography Discussion Group a t Denver, Colo., August 11-14, 1980.
Determination of Atmospheric Sulfur Dioxide without Tetrachloromercurate(I1) and the Mechanism of the Schiff Reaction Purnendu K. Dasgupta," Kymron DeCesare, and James C. Ullrey California Primate Research Center, University of California, Ua vis, California
Formaldehyde ( 7 mM) buffered at pH - 4 is used to stabilize atmospheric SO2 as hydroxymethanesulfonic acid. Equilibrium data for the above reaction are presented. Sulfite, liberated from the compound by base, is added to acidic pararosaniline for color development by the Schiff reaction, and absorbance is measured at 580 nm. The procedure has been optimized with regard to acidity and reagent concentrations. The method is comparable to the West-Gaeke method (Anal. Chern. 1956, 28, 1816) in absorption and recovery efficiency, sensitivity, and precision. No unusual interferences are observed due to 03,NO,, and transition-metal ions, except Mn(I1). A novel ion chromatographic procedure to determine hydroxymethanesulfonate and sulfate in the same sample is also described. Enhancement of sensitivity in the colorimetric method by solvent extraction has been studied. Investigations into the mechanism of the Schifi reaction and structure of the products have established the validity of the alkylsulfonic acid theory. Mechanistically an arninocarbinol seems to be the first intermediate, which undergoes subsequent nucleophilic substitution by bisulfite ion. To account for the high absorptivity of the product, we suggest that the sulfonic acid group is significantly ionized.
I n 1866, Schiff ( I ) reported the color regeneration in a SO2-bleached fuchsin solution upon the addition of an aldehyde. Extensive application of the Schiff reagent (fuchsin-sulfurous acid) to identify carbonyl compounds was pioneered by Schmidt (2) and identification of other functional groups, which can be oxidized to the carbonyl moiety, was introduced by Bauer ( 3 ) and McManus ( 4 ) . Kasten (5) and P e a c e (6) have adequately reviewed the histologic applications of this uniquely important reaction in histochemistry. Steigmann (7) turned the reaction around and utilized acid bleached fuchsin and formaldehyde for the qualitative identification of sulfites; a quantitative procedure by Grant ( 8 ) followed. Kozlyaeva (9) reported the determination of airborne SOz and used evacuated flasks for collection. Atkin ( I O ) used an alkaline glycerol solution, an absorber first described by Haller ( I I ) , to determine relatively high levels of SO?. Urone and Boggs (12) reduced the alkali content of Haller's absorber by a factor of 25 and described the first useful method for measuring ambient levels of SO1 (13, 1 3 ) . It !\a0.1 AU). Measurements were made near the absorption maxima wherever possible, but in most cases this was located beyond measuring range (