Detecting Airborne PAHs Using Thermal Desorption and GC–MS/MS
Scientists from the California Department of Public Health in Richmond, California, recently tested a new method for determining polycyclic aromatic hydrocarbons (PAHs) in gas phase airborne samples, combining thermal desorption (TD) and gas chromatography–tandem mass spectrometry (GC–MS/MS). Their findings were published in the Journal of Chromatography A (1).
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Polycyclic aromatic hydrocarbons are a group of chemical compounds made of multiple fused aromatic rings. They can occur naturally in coal, crude oil, and gasoline, but they can also be made when burning coal, oil, gas, and other flammable materials (2). PAH exposure can contribute to asthma and chronic obstructive pulmonary disease, with children being particularly vulnerable. In addition, occupational and environmental PAH exposure can increase one’s risk of lung cancer. Due to a wide range of molecular weights and boiling points, PAHs can be distributed between gas and particulate-bound phases in the air, depending on an individual PAH’s physical properties and environmental conditions, such as temperature and humidity. While many studies focus on particulate-bound PAHs, gaseous PAHs can have a significant role in human health, which may be underestimated if not properly considered (1).
PAH concentrations in air are typically low, reaching levels at or below sub ng/m3. As such, different challenges arise with getting temporal and spatial resolution data for these critical pollutants, mainly stemming from the complexity of sampling and the analytical procedures, which can impede progress in assessing health issues associated with PAH exposure.
In this study, the scientists created a solvent-free thermal extraction method for analyzing PAHs in gas-phase airborne samples. A fully automated thermal desorber, which utilizes flowing gas to extract a small heated solid or liquid sample, was coupled with GC–MS/MS to determine the concentration of trace level PAHs (3). Air sampling was conducted to tune the sampling and analytical conditions, with various instrument operating parameters, such as sorbent tube desorption temperature/time, cold trap desorption temperature/time, and outlet split ratio, being tested to optimize the analytical conditions.
The method’s performance showed linearity in a broad range (0.01 to 10 ng) with regression coefficients of external calibration curves (R2) >0.998 for all targeted PAHs. The method detection limit (MDL) ranged between 0.01–0.05 ng per tube. The precision (<20%) and accuracy (mean values between 80 and 120%) also proved satisfactory, obtaining quantitative recoveries. The method was successfully applied to outdoor and indoor air analysis, with small volumes of air sample (<144 L) being sufficient for PAH analysis.
For both indoor and outdoor air, the primary gaseous PAHs found were naphthalene, 1-methylnaphthalene, 2-methylnaphthalene, anthracene, fluoranthene, acenaphthene, fluorene, pyrene, and acenaphthylene. Naphthalene and its two methylated compounds, 1-methylnaphthalene and 2-methylnaphthalene, accounted for 47.7% and 81.7% of the total gas phase PAHs for outdoor and indoor, respectively.
Overall, using thermal extraction for the sample pretreatment instead of organic solvent extraction proved successful, making the method sustainable and work in consonance with green chemistry principles. Further, no solvent or time-consuming extract steps were necessary. This approach for sample pretreatment proved highly effective in enhancing the analytical process when combined with a fully automated TD-GC–MS/MS method.
References
(1) Wang, P.; Wang, Z-M.; Wagner, J.; Kumagai, K. A Solvent-Free Thermal Desorption-Gas Chromatography-Tandem Mass Spectrometry Method (TD-GC–MS/MS) for the Determination of Polycyclic Aromatic Hydrocarbons in Gas Phase Airborne Samples. J. Chromatogr. A 2025, 1744, 465689. DOI: 10.1016/j.chroma.2025.465689
(2) Polycyclic Aromatic Hydrocarbons (PAHs). CDC 2014. https://www.epa.gov/sites/default/files/2014-03/documents/pahs_factsheet_cdc_2013.pdf (accessed 2025-2-18)
(3) Thermal Desorption. ScienceDirect 2000. https://www.sciencedirect.com/topics/chemical-engineering/thermal-desorption (accessed 2025-2-18)
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