Dual-Mode Extraction with pH as the Link for Selective Enrichment of Perfluoroalkyl Acids Based on Layered Double Hydroxides and Switchable Hydrophilicity Deep Eutectic Solvent

In this work, a dual-mode extraction method based on soluble layered double hydroxides (LDHs) and switchable hydrophilic deep eutectic solvents (SHDESs) was developed with pH as a link. The method ingeniously used LDHs to capture perfluoroalkyl acids (PFAAs) by electrostatic and hydrogen-bond interactions, followed by LDH dissolution and simultaneous polarity switching of SHDES, achieving homogeneous extraction without a cumbersome phase-separation step. In addition, the fluorophilic SHDES provided remarkable selectivity for PFAAs because of the F-F interactions while eliminating coexisting anion interference. Combined with LC-MS/MS analysis, the approach achieved desirable performance with low detection limits (0.07-0.40 ng/L) and satisfactory recovery (85.8-118.9%). More importantly, the underlying mechanisms were systematically elucidated through spectroscopic techniques, density functional theory, and molecular dynamics simulation. Therefore, this work established a significant sample pretreatment platform, offering an efficient and reliable avenue for trace component analysis.