title: Determination of polydimethylsiloxane-water partition coefficients for ten 1-chloro-4-[2,2,2-trichloro-1-(4-chlorophenyl)ethyl]benzene-related compounds and twelve polychlorinated biphenyls using gas chromatography/mass spectrometry.
abstract: Polymer-water partition coefficients (Kpw) of ten DDT-related compounds were determined in pure water at 25 °C using commercial polydimethylsiloxane-coated optical fiber. Analyte concentrations were measured by thermal desorption-gas chromatography/full scan mass spectrometry (TD-GC/MSFS; fibers) and liquid injection-gas chromatography/selected ion monitoring mass spectrometry (LI-GC/MSSIM; water). Equilibrium was approached from two directions (fiber uptake and depletion) as a means of assessing data concordance. Measured compound-specific log Kpw values ranged from 4.8 to 6.1 with an average difference in log Kpw between the two approaches of 0.05 log units (∼ 12% of Kpw). Comparison of the experimentally-determined log Kpw values with previously published data confirmed the consistency of the results and the reliability of the method. A second experiment was conducted with the same ten DDT-related compounds and twelve selected PCB (polychlorinated biphenyl) congeners under conditions characteristic of a coastal marine field site (viz., seawater, 11°C) that is currently under investigation for DDT and PCB contamination. Equilibration at lower temperature and higher ionic strength resulted in an increase in log Kpw for the DDT-related compounds of 0.28-0.49 log units (61-101% of Kpw), depending on the analyte. The increase in Kpw would have the effect of reducing by approximately half the calculated freely dissolved pore-water concentrations (Cfree). This demonstrates the importance of determining partition coefficients under conditions as they exist in the field.
authors.affiliation: U.S. Geological Survey, Reston, Virginia 20192, United States. Electronic address: eganhous@usgs.gov.
authors.forename: Robert P
authors.initials: RP
authors.lastname: Eganhouse
mesh_terms: D004129:Dimethylpolysiloxanes / Q000737:chemistry*; D004784:Environmental Monitoring / Q000379:methods*; D008401:Gas Chromatography-Mass Spectrometry; D011078:Polychlorinated Biphenyls / Q000032:analysis*; D015203:Reproducibility of Results; D012623:Seawater / Q000737:chemistry; D014867:Water / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D004129:Dimethylpolysiloxanes; D014874:Water Pollutants, Chemical; D014867:Water; D011078:Polychlorinated Biphenyls
keywords: DDT; PCB; PDMS–water partition coefficients (K(pw)); SPME; Seawater; Solid-phase microextraction