Non-Target Analytical Workflow for Gas-Phase Atmospheric Chemicals Collected on XAD Resin and Application to Passive Samplers

Abstract

The atmospheric gas phase is underrepresented in non-target screening of environmental organic chemicals, partly due to limited evidence on sorbent suitability. Here, we developed a workflow for non-target analysis (NTA) of styrene-divinylbenzene copolymeric (XAD) resin-based air samples that involves both gas (GC) and liquid chromatography (LC) high-resolution mass spectrometry (HRMS). More than 60 000 features were detected in passive air samplers (PAS) deployed over 4–48 weeks. Of ∼34 000 features retained after blank filtration, ∼14 000 (41%) showed an increasing signal with deployment time, suggesting that they represent substances with volatility and degradability sufficiently low for accumulation on XAD without substantial re-evaporation or degradation during the prolonged sampling period. Such linear uptake is a prerequisite for comparing PAS-derived signals across deployments and chemical classes. Chemical identification by reference standards (level 1) and spectral library matching (level 2) initially identified/annotated 116 compounds, many of which were bioactive and/or brown carbon species. Combining advanced downstream computational workflows of feature-based molecular networking (FBMN) and in silico prediction (Network Annotation Propagation/MetFrag) allowed for the structural annotation (level 3) of >8300 LC-HRMS features, including several compounds of natural and anthropogenic origin which were not previously reported in the atmospheric gas phase. Several long-chain fatty acids showed rapid early increases implausible with atmospheric origins and are likely to originate from microbial growth on the resin. Overall, our results demonstrated that XAD is a sorbent compatible with comprehensive NTA and suitable for time-integrated passive sampling of a diverse range of gas-phase organic chemicals from the atmosphere.