Method for measuring air-immiscible liquid partition coefficients

The principal objective of this work was to measure nonaqueous phase liquid-air partition coefficients for various gas tracer compounds. Known amounts of trichloroethene (TCE) and tracer, as neat compounds, were introduced into glass vials and allowed to equilibrate. The TCE and tracer concentration of the headspace was analyzed and the partition coefficient was calculated from a mass balance. The TCE-air partition coefficient, defined as the ratio of the concentration of the tracer in the vapor phase to its concentration in the TCE phase, for gas tracer compounds perfluorodimethylcyclobutane, perfluoromethylcyclopentane, perfluoromethylcyclohexane, dibromodifluoromethane, and dibromotetrafluoroethane were determined to be 22, 24, 53, 370, and 470 for temperatures of 22-28°C. Most of the variability follows from uncertainty with measurements of tracer vapor-phase concentrations, with overall relative percent differences ranging from 8.5 to 25%. This methodology produces results consistent with literature values obtained from column tests, with similar reproducibility.