Enhancing Detection of Per- and Polyfluoroalkyl Substances via Pore-Microenvironment-Engineered Hierarchical Porous Covalent Organic Frameworks-Based Probe Nanoelectrospray Ionization Mass Spectrometry

It is of great significance yet challenging to develop state-of-the-art solid-phase microextraction (SPME) adsorbents to selectively enrich per- and polyfluoroalkyl substances (PFASs) in a complex environment before ultrasensitive analysis. Herein, for the first time, covalent organic frameworks (COFs) (termed COF-A, COF-QA, and COF-IM) with outstanding hierarchical porous structures were delicately constructed via a pore-environment engineering strategy through rationally appending synergistic electrostatic/hydrophobic affinity groups featuring similar lengths of carbon chains but distinctive cationic functional sites onto pore walls. Coupled with the cutting-edge nanoelectrospray ionization mass spectrometry, these COFs-based SPME probes were thoroughly explored for highly selective enrichment and ultrasensitive simultaneous discrimination of trace PFASs. Notably, COF-IM exhibited the most remarkable enrichment factor, realizing the rapid determination of eight investigated PFASs (about 4 min) with low limits of detection (0.06 to 0.13 ng L^-1) and quantification (0.20 to 0.42 ng L^-1), and a wide linear range of 1-5000 ng L^-1 (<i>R</i>² of 0.999-0.9998). The method developed has been successfully applied to real samples (tap water, lake water, spring water, ocean water, and blood) with satisfactory recoveries (75.1-112.9%). All of these features demonstrated that pore-microenvironment engineering of COFs-SPME probes is a promising and effective strategy for the rapid, selective and ultrasensitive determination of PFASs in real applications.