title: Isotope fractionation of benzene during partitioning - Revisited.
abstract: Isotope fractionation between benzene-D0and benzene-D6caused by multi-step partitioning of the benzenes between water and two organic solvents, n-octane and 1-octanol, as well as between water and the gas phase, was measured. The obtained fractionation factors αH = KH/KDare αH = 1.080 ± 0.015 and αH = 1.074 ± 0.015 for extraction into n-octane and 1-octanol, respectively, and αH = 1.049 ± 0.010 for evaporation from aqueous solution. The comparison of solvent- and gas-phase partitioning reveals that about 2/3 of the driving force of fractionation is due to different interactions in the aqueous phase, whereas 1/3 is due to different interactions in the organic phase. The heavy benzene isotopologue behaves more 'hydrophilically' and the light one more 'hydrophobically'. This synergistic alignment gives rise to relatively large fractionation effects in partitioning between water and non-polar organic matter. In contrast to a previous study, there is no indication of strong fractionation by specific interactions between benzene and octanol. Partitioning under non-equilibrium conditions yields smaller apparent fractionation effects due to opposite trends of thermodynamic and kinetic fractionation parameters, i.e. partition and diffusion coefficients of the isotopologues. This may have consequences which should be taken into account when considering isotope fractionation due to sorption in environmental compartments.
authors.affiliation: Department of Environmental Engineering, Helmholtz Centre for Environmental Research - UFZ, Leipzig D-04318, Permoser Straße 15, Germany. Electronic address: frank-dieter.kopinke@ufz.de.
authors.forename: F-D
authors.initials: FD
authors.lastname: Kopinke
authors.affiliation: Department of Environmental Engineering, Helmholtz Centre for Environmental Research - UFZ, Leipzig D-04318, Permoser Straße 15, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Georgi
authors.affiliation: Laboratory of Hydrology and Geochemistry of Strasbourg (LHyGeS), University of Strasbourg/ENGEES, UMR 7517 CNRS, France.
authors.forename: G
authors.initials: G
authors.lastname: Imfeld
authors.affiliation: Department of Biogeochemistry, Helmholtz Centre for Environmental Research - UFZ, Leipzig D-04318, Germany.
authors.forename: H-H
authors.initials: HH
authors.lastname: Richnow
mesh_terms: D001554:Benzene / Q000737:chemistry*; D005591:Chemical Fractionation; D003903:Deuterium / Q000737:chemistry*; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D014874:Water Pollutants, Chemical; D003903:Deuterium; D001554:Benzene
keywords: Diffusion; Evaporation; Isotopic fractionation; Partitioning; Solute-solvent interactions; Solvent extraction