TAPB-DHTP functionalized cotton fiber for in-syringe solid-phase extraction and determination of fluoroquinolones in food samples.

Trace residues of fluoroquinolones (FQs) in food matrices are difficult to determine directly because of their low concentrations and the complexity of protein- and sugar-rich samples. In this work, cotton fibers functionalized with a TAPB-DHTP covalent organic framework (TAPB-DHTP COF@cotton) were prepared as a packed adsorbent for in-syringe solid-phase extraction (IS-SPE) of FQs. (3-aminopropyl)triethoxysilane (APTES) was first grafted onto cotton fibers through condensation between the ethoxy groups of APTES and the surface hydroxyl groups of cotton, introducing amino groups onto the fiber surface. TAPB-DHTP COF was then grown in situ on the APTES-modified fibers through Schiff-base condensation between TAPB and DHTP. This design combines the easy packing and flexibility of cotton fibers with the rough surface and adsorption sites provided by the COF coating. The obtained material was characterized using several instrumental techniques. After coupling with ultra-performance liquid chromatography, the method was used for the determination of enoxacin, levofloxacin, and ciprofloxacin. Under the optimized extraction conditions, the method showed good linearity over 0.5-100 ng/mL, with correlation coefficients of 0.9991-0.9996. The limits of detection were 0.02-0.08 ng/mL, and the intra-batch and inter-batch relative standard deviations (RSDs) were below 4.66% and 4.85%, respectively. The extraction efficiencies and enrichment factors were 76.9-83.8% and 51.31-55.84. The method was applied to honey, egg white, and fish samples, giving recoveries of 81.05-97.23% with RSDs below 9.77%. The results demonstrate that TAPB-DHTP COF@cotton provides a practical fibrous adsorbent for trace fluoroquinolone determination in complex food matrices.