Field demonstration for the solvent-based sampling method to perform compound-specific isotope analysis on gas-phase...

Area of Science:

• Environmental Chemistry
• Isotope Geochemistry
• Analytical Chemistry

Background:

• Volatile organic compounds (VOCs) are significant environmental contaminants.
• Compound-specific isotope analysis (CSIA) is a powerful tool for source identification and fate studies.
• Accurate sampling methods are crucial for reliable CSIA of gas-phase VOCs.

Purpose of the Study:

• To evaluate a novel solvent-based sampling method for collecting gas-phase VOCs for CSIA.
• To assess the method's reliability in providing precise and accurate carbon isotope (δ¹³C) measurements.
• To compare isotopic values of gaseous VOCs with their source material (NAPL) and groundwater.

Main Methods:

• A controlled field study was conducted using a synthetic hydrocarbon source.
• Methanol was used as a solvent to accumulate petroleum hydrocarbons from soil air and effluent gas.
• Carbon isotope analysis (δ¹³C) was performed on five specific VOCs (benzene, toluene, o-xylene, cyclopentane, octane).

Main Results:

• The solvent-based method demonstrated the capacity to produce precise and accurate δ¹³C measurements.
• Isotopic discrepancies between gaseous VOCs and the NAPL source were minimal (<1‰) for most samples.
• This study is the first to report δ¹³C measurements for up to five gas-phase VOCs from a single sample.

Conclusions:

• The solvent-based sampling method is reliable for CSIA of gas-phase VOCs.
• The method's ability to analyze multiple VOCs strengthens the assessment of connections between gaseous VOCs and their sources.
• This methodology supports the application of CSIA in VOC vapor studies and forensic investigations.