Identification and semi-quantification of alkylated polycyclic aromatic hydrocarbons in PM2.5 filter samples using in-injection port thermal desorption coupled with two-dimensional gas chromatography and rapid-scanning quadrupole mass spectrometry (TD-GC×GC-qMS)

Abstract

Growing evidence suggests that alkylated derivatives of polycyclic aromatic hydrocarbons (PAHs) should be considered in toxicity assessment, necessitating their identification and quantification in ambient air. In this work, we explored the effectiveness of in-injection port thermal desorption coupled with two-dimensional gas chromatography and rapid-scanning quadrupole mass spectrometry (TD-GC × GC-qMS) to detect alkylated PAHs. The reliability of compound identification was carefully evaluated based on detection frequency, retention time consistency, mass spectra similarity to NIST library, and sample-to-sample mass spectral variations. Leveraging the technique's ability to determine low-concentration compounds from complex matrices and to aid in the recognition of homologues via visual inspection, we identified 104 alkylated PAHs in PM_2.5 samples collected in Beijing, China. These include 3-ring and 4-ring PAHs with a higher level of alkylation of 3–4 carbon atoms. Our results demonstrated the presence of diverse isomeric structures of alkylated PAHs in ambient PM_2.5, with their concentrations exceeding those of their parent PAHs for smaller PAHs but being lower for larger ones. The contribution of alkylated PAHs to the health risk of PAHs was around 5 % in our samples using the toxicity equivalency factor method. The findings of this study underscore the importance of alkylated PAHs in PM_2.5 and highlight the potential of TD-GC × GC-qMS in advancing research on profiling toxicants in atmospheric aerosols. Given the widespread availability of qMS and the ease of implementing GC × GC through a solid-state thermal modulator, we recommend the adoption of TD-GC × GC-qMS in the analysis of aerosol samples. This approach enables quantification and isomer-specific analysis of a broader range of alkylated PAHs with improved accuracy.