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.