Rational design of fluorinated covalent organic framework coatings for high-performance SPME of isoxazoline...

Novel isoxazoline-class veterinary drugs have been widely adopted as broad-spectrum acaricides and insecticides in veterinary medicine. Herein, a new fluorine-functionalized covalent organic framework was designed and synthesized. The fluorinated framework exhibits significantly enhanced adsorption capacity for isoxazoline compounds compared to its non-fluorinated analogue, attributable to multiple synergistic interactions including pseudo-hydrogen bonding, F-O, F-π interactions, π-π stacking, and enhanced hydrophobic effects between the fluorinated COF and isoxazoline molecules. The COF-functionalized SPME fibers were fabricated for the enrichment of isoxazolines from complex water and milk samples, followed by sensitive LC-MS/MS quantification. Under optimized conditions, the developed SPME/LC-MS/MS method exhibited wide linearity (0.01-50 ng mL^-1, R² ≥ 0.9935), satisfactory recoveries (81.7-118.6%) with RSDs of 3.0-8.1%, and demonstrated high sensitivity and selectivity. This analytical approach reports the first application of SPME for detecting novel isoxazoline drugs in milk and water matrices, offering significant promise for advancing food safety surveillance and environmental monitoring programs.