Hydrophobic covalent organic frameworks for solid-phase microextraction of pyrethroids

Two hydrophobic covalent organic frameworks (COFs), BTT-TAPA-COF and BTT-TAPB-COF, were synthesized using benzotrithiophene (BTT), a fused heterocyclic building block. These COFs exhibited high porosity (BET surface areas of 763 and 1531 m²/g) and strong hydrophobicity (contact angles of 118.5° and 127.5°). BTT-COFs were coated onto stainless-steel fibers and employed in solid-phase microextraction (SPME) coupled with GC-MS for pyrethroids detection in tea. Direct immersion (DI-SPME) achieved 200-fold higher extraction efficiency than headspace (HS-SPME). Epoxy resin was identified as the optimal adhesive for fiber preparation. The method demonstrated dual linear dynamic ranges for each analyte, with correlation coefficients (R²) ranging from 0.9852 to 0.9999 and LODs as low as 0.002 ng·L⁻¹. Bifenthrin (BIF) and λ-cyhalothrin (CYH) were detected in all tested tea samples, at concentrations ranging from 7.9 - 98.2 ng·L⁻¹ and 1.2 - 4.2 ng·L⁻¹, respectively. The method exhibited satisfactory recoveries from 81.1% to 125.8%. This study highlights the potential of hydrophobic COFs as high-performance SPME materials for sensitive and reliable pesticide residue determination in food safety monitoring.