Measurement of Henry's Constants of High-Volatility Organic Compounds Using a Headspace Autosampler

A method using a headspace autosampler and gas chromatograph (GC) was developed to measure Henry's law constant of volatile organic compounds (VOCs). Equilibrium of VOCs between gas and liquid was established in the 22-mL headspace glass vials sealed with Teflon-faced silicone septa and cramp aluminum caps. Equilibration, sampling, and chemical concentration analysis by a high precision headspace autosampler−GC system minimize sample losses due to volatilization and give accurate results. The method uses several different gas−liquid volume ratios in the headspace vials to create different equilibrium concentrations in the gas phase. With data of the chemical concentration in gas versus the different gas−liquid volume ratio, Henry's constant is determined by regression analysis of a headspace system equation derived from mass balance principle and ideal gas law. Henry's constants for benzene, toluene, trichloroethylene, and tetrachloroethylene at 15, 20, 25, 30, 35, 40, and 45 °C were measured with this method and compared with literature data.