Efficient online enrichment of fluorinated liquid crystal monomers by imine covalent organic frameworks

Fluorinated liquid crystal monomers (FLCMs), widely used in electronic display technologies, have recently attracted increasing attention as emerging environmental contaminants, while their accurate determination in complex environmental matrices remains challenging. Herein, three crystalline imine-linked covalent organic frameworks (COFs) with systematically varied fluorination degrees (0F-COF, 1F-COF, and 3F-COF) were constructed and integrated as sorbents into an online fluorous solid-phase extraction coupled with high-performance liquid chromatography-ultraviolet detection (FSPE-HPLC-UV) platform. Structure-performance correlations revealed that 1F-COF achieved superior extraction performance by balancing pore structure with fluorine-regulated interfacial interactions, thereby enabling efficient enrichment of fluorinated analytes. Under optimized conditions, enrichment factors (EFs) of 135-272 were obtained, with detection limits of 0.15-0.33 ng mL⁻¹ and good linearity over 0.5-100 ng mL⁻¹. The 1F-COF SPE cartridge retained stable performance over 60 extraction-elution cycles. The method was validated in water and soil samples with recoveries of 84.3-108.7%. This work establishes fluorine-regulated COFs as effective sorbents for online FLCM enrichment and provides a practical HPLC-UV strategy for environmental monitoring.