Exploring the fluorinome of PFAS-impacted groundwater using 21 tesla FT-ICR mass spectrometry

Non-targeted analysis of complex per- and polyfluoroalkyl substances (PFAS) via Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) promises unprecedented insights into the "fluorinome", i.e., the complete set of organofluorine compounds in a given sample. In this study, we present a Python-based workflow developed in parallel with a carefully constructed PFAS formula database comprising ∼ 20 million entries to facilitate the assignment of chemical formulas to ultrahigh-resolution mass spectra. PFAS assignments based on the analysis of complex aqueous film-forming foam (AFFF) on the world's highest-resolving 21 tesla FT-ICR MS were compared to quadrupole time-of-flight (QTOF) MS data, validating 22 common and discovering 19 previously undetected PFAS classes. We then explored the viability of ultrahigh-resolution FT-ICR MS analysis for forensic profiling purposes on PFAS-impacted groundwater samples, identifying bis-perfluoroalkyl sulfonimides (bis-FASIs) as long-suspected ingredients of electrochemical fluorination AFFFs. While our newly developed workflow may also be used for other types of high-resolution mass spectrometers such as QTOF and Orbitrap, this work leverages the unique ultrahigh-resolving power, sub-ppm mass measurement accuracy, and high dynamic range of 21 tesla FT-ICR mass spectrometry to maximize information from complex contaminant mixtures in environmental samples.