A relative headspace method for Henryʹs constants of volatile organic compounds

A relative headspace gas chromatographic method is described for the measurement of Henryʹs constants of volatile organic compounds (VOCs) in aqueous salt solutions. The method requires the Henryʹs 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. Henryʹs 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 Henryʹs 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 Henryʹs constant data over the entire range of salt concentrations.