title: The pseudophase approach to assessing chemical partitioning in air-water-cyclodextrin systems.
abstract: Henry's Law constants (HLCs) of several common, subsurface hydrophobic organic pollutants (HOPs) including trichloroethylene (TCE), perchloroethylene (PCE) and benzene, toluene, ethylbenzene, and o-xylene (BTEX), were measured using a static headspace phase ratio (SHPR) method over a range of temperatures (35, 45, 55, and 65 degrees C) and experimentally and operationally relevant cyclodextrin (CD) concentrations (0, 10, 20, 50, and 100 g L(-1)). In aqueous CD solutions, HLC values decrease according to a power law relationship with increasing CD concentration due to an apparent solubility enhancement caused by HOP partitioning to the hydrophobic cavity of CD molecules. The temperature dependence of air-water partitioning under the influence of CD was well described by the van't Hoff equation for all HOPs tested. A three-phase equilibrium model was used to interpret air-water-CD partitioning data, treating CD as a pseudophase. Our results show that HOP CD-water partition coefficients decrease linearly with increasing temperature. CD-water partition coefficients were generally independent of CD concentration, with a few exceptions. Comparison of our results for hydroxypropyl-beta-CD and TCE to those from another study showed several major discrepancies, which were attributed to differences in the experimental methods employed. Our attempt to correlate CD-water partition coefficients with HOP chemical properties indicates that correlations based on individual chemical descriptors (e.g., aqueous solubility, octanol-water partition coefficient, molecular volume or ET (30) polarity index) will not be sufficient to obtain accurate estimates of HOP CD-water partition coefficients for other compounds with differing chemical structures.
authors.affiliation: Department of Civil and Environmental Engineering, 3418 Patrick F. Taylor Hall, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
authors.forename: Heng
authors.initials: H
authors.lastname: Gao
authors.forename: William J
authors.initials: WJ
authors.lastname: Blanford
authors.forename: Justin E
authors.initials: JE
authors.lastname: Birdwell
mesh_terms: D000388:Air; D003505:Cyclodextrins / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D003505:Cyclodextrins; D014867:Water