Determination of Atmespheric Sulfur Dioxide without Tetrachloromercurate(II) and the Mechanism of the Schiff Reaction

Article abstract of DOI:10.1021/ac50062a031

Formaldehyde (7mM) buffered at pH aprox. 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.Chem. 1956, 28, 1816) in absorption and recovery efficiency, sensitivity, and precision.No unusual interferences are observed due to O3, NO2, and transition-metal ions, except Mn(II).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.Investigation into the mechanism of the Shiff reaction and structure of the products have established the validity of the alkylsulfonic acid theory.Mechanistically an aminocarbinol seems to be the first intermediate, which undergoes subsequent nucleophillic substitution by bisulfite ion.To account for the high absorptivity of the product, we suggest that the sulfonic acid group is significantly ionized.