Real-time identification of airborne per- and polyfluoroalkyl substances (PFAS) using chemical ionization mass spectrometry (CIMS) with nitrate (NO3-) reagent ion

Per- and polyfluoroalkyl substances (PFAS) are anthropogenic chemicals that pose significant risk to human health and the environment. Due to their strong carbon-fluorine (C-F) bonds, PFAS are persistent and continue to cycle through temporary environmental sinks (e.g., air) across the globe long after their release. The atmospheric fate of PFAS is poorly understood due to limited analytical methods to probe their temporal dynamics. Chemical ionization mass spectrometry (CIMS) can help resolve the sources, transformations, and movement of airborne PFAS by providing high-sensitivity measurements of trace gas-phase species in real-time using reagent ions of varying selectivity. Current CIMS methods, including iodide (I-) and superoxide(O2-) CIMS, are ideal for detecting semi-volatile PFAS, but less sensitive towards lower-volatility PFAS. Nitrate (NO3-) CIMS has shown great sensitivity towards extremely low-volatility oxygenated vapors, making it an ideal candidate for identifying low-volatility PFAS such as oxidation products of precursor PFAS. In this feasibility study, NO3-CIMS was found to be sensitive towards many PFAS subclasses, including PFCAs and PFSAs, and had ppqv sensitivity towards PFBA, an ultra-short chained PFCA of regulatory interest. This is the first use of NO3-CIMS for PFAS detection, as well as for general quantification of airborne species. Additionally, the first real-time detection of gas-phase PFOS, a toxic legacy PFSA with continued environmental persistence, is reported.