Measurement of Stable Carbon Isotope Ratio of Volatile Organic Compounds Using Thermal Desorption-Gas Chromatography-Combustion-Isotope Ratio Mass Spectrometry.

This paper presents a method combining a thermal desorption (TD) unit with gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) to determine compound specific δ13C values of seven VOCs (benzene, toluene, ethylbenzene, m/p-xylene, o-Xylene, styrene, and cumene). The main innovation lies in the systematic validation of TD-GC-C-IRMS for atmospheric VOC analysis, which enables reliable δ13C determination with minimal isotopic bias. The optimal TD conditions were 300°C and 5 min. Advantages include high precision (SD ≤ 0.4‰), good reproducibility, long-term sample stability (up to 50 days), and suitability for on-site air sampling. Limitations are the coverage of only seven compounds and a wider range of VOC species and more complex matrices should be addressed in future work. The method was successfully applied to ambient air samples, and isotopic signatures indicated that VOCs were mainly derived from traffic-related emissions. This approach provides a robust and practical tool for source identification of atmospheric VOCs and supports source apportionment studies in environmental research.