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

Position-specific isotope effects (PSIEs) have been measured by isotope ratio monitoring 13C 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 ...