Stable Carbon Isotope Ratio of Volatile Organic Compounds in Air Using Solid-Phase Microextraction Coupled with Chromatography, Combustion, and Isotope Ratio Mass Spectrometry

The isotopic analysis of atmospheric volatile organic compounds (VOCs), and in particular their carbon isotope ratio (δ13C), has the potential to be an effective tool for clearly identifying sources of these pollutants. However, to date, there have been very few such analyses. In the work described herein, we have attempted to analyze the δ13C values of VOCs using solid-phase micro-extraction (SPME) coupled with chromatography, combustion, and isotope ratio mass spectrometry (SPME-GC/C/IRMS). The collection and equilibration of VOCs on an SPME fiber required approximately 700−800 min. Although this sample acquisition time is relatively long, extraction and analysis could be achieved reasonably rapidly. The δ13C values of benzene, trichloroethylene, toluene, tetrachloroethylene, ethylbenzene, m,p-xylenes, styrene, and o-xylene in a 200 ppb standard gas determined by SPME-GC/C/IRMS ranged from − 29.7‰ to − 22.9‰. The standard deviations ranged from ± 0.4 to ± 1.6‰, and were thus very reasonable compared to those in other studies. In addition, we tested air samples with concentrations ranging from 5 to 500 ppb. In general, because the reasonable precision of GC/C/IRMS is < 0.2‰, the required area of SPME-GC/C/IRMS ranged from 12 Vs (o-xylene) to 50 Vs (m,p-xylenes). The δ13C values of benzene for vehicle exhaust and in the vicinity of a gas station were − 25.3 ± 1.0‰ and − 26.2 ± 0.7‰, respectively. Compared with other references, the data in this study were reasonable. The detected differences between gasoline and vehicle emissions were similar to those in previous research. Our δ13C value of benzene for vehicle exhaust closely resembled values in the vicinity of a gas station. This narrow range may have been because vehicle exhaust samples in this research were collected in cold start mode rather than hot mode. Benzene in gasoline can be emitted through the tail pipe due to inactivity of the catalyst in cold mode.