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Multistep Partitioning Causes Significant Stable Carbon and Hydrogen Isotope Effects During Volatilization of Toluene and propan-2-ol From Unsaturated Sandy Aquifer Sediment

Multistep Partitioning Causes Significant Stable Carbon and Hydrogen Isotope Effects During Volatilization of Toluene and propan-2-ol From Unsaturated Sandy Aquifer Sediment

Sarah Zamane, Didier Gori, Patrick Höhener

Chemosphere. 2020 Jul;251:126345.

PMID: 32169696

Abstract:

This study aimed at investigating whether stable isotopes can be used to monitor the progress of volatile organic compounds (VOCs) volatilization from contaminated sediment during venting. Batches of a dry aquifer sediment were packed into stainless steel HPLC columns, humidified with distilled water and later contaminated by either liquid toluene or propan-2-ol. The VOCs were then volatilized by a stream of gas at room temperature, and the concentrations and stable isotope ratios of gaseous VOCs were recorded by isotope-ratio mass spectrometry. During early stages of volatilization of toluene, the isotope ratios Δδ13C shifted to more negative values by about -3 to -5‰ and the Δδ2H by more than -40‰, while the concentration remained at or near initial saturated vapor concentration. Depletion of the isotope ratios in the gas was explained by the vapor-liquid fractionation process, which is amplified by successive self-partitioning steps of gaseous VOC into remaining liquid VOC. For propan-2-ol the carbon isotope shift was negative like for toluene, whereas the H shift was positive. Hydrogen bonding in the liquid propan-2-ol phase causes a normal vapor-liquid H isotope effect which was described already in classical literature. The isotope shifts in the present experiments are larger than previously reported shifts due to phase-change processes and reach the magnitude of shifts usually observed in kinetic isotope fractionation.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AS2121215	VOCs - Sediment 2			Price

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