A relative headspace method for Henry's constants of volatile organic compounds

A relative headspace gas chromatographic method is described for the measurement of Henry's constants of volatile organic compounds (VOCs) in aqueous salt solutions. The method requires the Henry's constant of the VOC in pure water, and employs larger liquid samples than conventional headspace techniques in order to minimize errors arising from solute mass loss from the liquid phase. Henry's constants of five methyl ketones (2-propanone, 2-butanone, 2-pentanone, 2-hexanone, and 2-heptanone) in 0.2 M (molal) to 1.0 M sodium sulfate solutions were measured using the relative method at temperatures between 50 and 80 °C. Reference values of Henry's constants of the five methyl ketones in pure water were measured using a differential headspace technique. The entire data set was correlated using an equation containing three parameters (obtained from VOC + water data) and a single salt parameter. The equation was able to successfully extrapolate Henry's constant data over the entire range of salt concentrations.