Water Radical Anion/Cation Pair-Induced C-F Activation for Sensitive Ambient Mass Spectrometry of Perfluoroalkanes

Perfluoroalkanes (PFAs), a subclass of per- and polyfluoroalkyl substances (PFASs), are persistent environmental contaminants of growing global concern. The combination of high carbon-fluorine (C-F) bond stability and the absence of ionizable groups makes the direct detection of PFAs highly challenging, typically requiring complex sample preparation. Herein, we report a novel online ambient mass spectrometry (MS) approach for the rapid and sensitive analysis of PFAs without any sample pretreatment. This approach utilizes a corona discharge source to generate reactive water radical anions/cations (H₂O^-•/H₂O^+•) in situ, which efficiently activate the inert C-F bond via a hydroxylation pathway, converting PFAs into readily detectable hydroxylated derivatives. The approach was demonstrated for perfluorooctane, perfluorohexane, and perfluoroheptane, achieving direct, real-time analysis, with limits of detection (LODs) ranging from 0.28 to 0.30 ng/L. The reaction mechanism and products were characterized using high-resolution MS, tandem MS, isotope labeling, and theoretical calculations. This H₂O^-•/H₂O^+•-induced strategy provides an efficient and powerful tool for the sensitive screening of PFAs in environmental samples.