Insights into Mechanistic Models for Evaporation of Organic Liquids in the Environment Obtained by Position-Specific Carbon Isotope Analysis

Abstract

Position-specific isotope effects (PSIEs) have been measured by isotope ratio monitoring (13)C nuclear magnetic resonance spectrometry during the evaporation of 10 liquids of different polarities under 4 evaporation modes (passive evaporation, air-vented evaporation, low pressure evaporation, distillation). The observed effects are used to assess the validity of the Craig-Gordon isotope model for organic liquids. For seven liquids the overall isotope effect (IE) includes a vapor-liquid contribution that is strongly position-specific in polar compounds but less so in apolar compounds and a diffusive IE that is not position-specific, except in the alcohols, ethanol and propan-1-ol. The diffusive IE is diminished under forced evaporation. The position-specific isotope pattern created by liquid-vapor IEs is manifest in five liquids, which have an air-side limitation for volatilization. For the alcohols, undefined processes in the liquid phase create additional PSIEs. Three other liquids with limitations on the liquid side have a lower, highly position-specific, bulk diffusive IE. It is concluded that evaporation of organic pollutants creates unique position-specific isotope patterns that may be used to assess the progress of remediation or natural attenuation of pollution and that the Craig-Gordon isotope model is valid for the volatilization of nonpolar organic liquids with air-side limitation of the volatilization rate.

Position-specific hydrogen isotope equilibrium in propane

“…This subject grew dramatically with the development of NMR techniques for measuring position-specific variations in D and 13 C abundances in organic molecules (Martin and Martin, 1981;Caytan et al, 2007). Such work has been applied to foodscience, plant physiology, paleoenvironment reconstruction and environmental contamination (Remaud et al, 1997;Gilbert et al, 2012;Ehler et al, 2015;Julien et al, 2015 and2016). Intramolecular isotopic fractionations can reflect temperatures of molecular synthesis, mechanisms of formation, and/or source substrates (Martin et al, 2008;Eiler, 2013b).…”

Simultaneous observation of concurrent two-dimensional carbon and chlorine/bromine isotope fractionations of halogenated organic compounds on gas chromatography

“…The measured Λ h E (Λ 37 Cl, Λ 81 Br and Λ 13 C) directly reflect the isotope fractionation magnitudes of the HOCs on GC. As shown in Figure 5, the Λ 37 Cl and Λ 81 Br were generally lower than the Λ 13 Interestingly, we unequivocally observed a gradually ascending tendency of Λ 13 C with the increase of bromine atoms on the molecules (from MoBB to HBB).…”

“…where IRTj represents the isotope ratio derived from the retention-time segment j; h E represents the heavy isotopes of interest ( 13 C, 37 Cl and 81 Br). △ h E > 0 and < 0 indicate inverse and normal isotope fractionations, respectively, while △ h E = 0 means no isotope fractionation.…”

“…The observed carbon isotope fractionation was generally more significant than the chlorine/bromine isotope fractionation, indicating that the total isotope effects of carbon were larger than those of chlorine and bromine. According to the literatures [30,37], the total isotope effects (IEtotal) can be expressed as:…”

“…We define the nominal molecular mass of a hypothesized chlorine/bromine isotopologue as m (isotopologue-0), then the molecular mass of the adjacent isotopologue containing one more 13 C atom is m+1 (isotopologue-1), and that of the adjacent isotopologue containing one more 37 Cl/ 81 Br atom is m+2 (isotopologue-2) [40]. Accordingly, the diffusive fractionation factor between isotopologue-0 and isotopologue-1 (αdiff-C) can be given by:…”