# Supramolecular Materials as Solid-Phase Microextraction Coatings in Environmental Analysis
## 4 Covalent Organic Frameworks (COFs)
### COFs as SPME Coatings for Environmental Applications
#### 4.3.4 Extraction of Pesticides and Insecticides from Water Samples  
The use of COFs as key materials for SPME devices has been proposed as a valid alternative to the MOF-based coatings (described in Section 3.3.3), and also for the selective extraction of OCPs and OPPs at trace levels in environmental matrices [123; 124; 125; 126]. [PERSON] and coworkers developed a ketoenamine COF (Tp\(-\)Azo\(-\)COF) to be used as an SPME coating for the extraction of OCPs [123]. The COF was obtained by solvothermal treatment and deposited onto etched SS wires using an epoxy resin. The adsorbent material showed a high percentage (5.8%) of electronegative N atoms, facilitating the formation of halogen bonds between the analytes and the coating, a BET area of 1218 m\({}^{2}\)/g, and high porosity, with a total pore volume of 0.689 m\({}^{3}\)/g. The Tp\(-\)Azo\(-\)COF-coated fiber exhibited higher EFs compared to commercial fibers, ranging from 1061 to 3693 for the five investigated OCPs. DI-SPME sampling using this fiber followed by GC-MS/MS analysis of OCPs resulted in LOQs in the 0.005-0.26 ng/L range and good precision (RSDs \(<\) 11%). Green tea, milk, tap, and well water samples were analyzed by the validated DI-SPME-GC-MS/MS method: no analyte was detected in real samples, whereas recoveries in the 83.4\(-\)101.6% range were obtained on spiked matrices. A novel porous COF coating synthesized by condensation between cyanuric chloride, 4,4\({}^{\prime}\)-ethylendianiline, and 3,4,9,10-perylenetetracarboxylic di-anhydride was devised by [PERSON] and [PERSON] [124]. The COF was deposited onto SS wires using a silicon glue solution. The DI-SPME extraction was coupled with GC-CD-IMS analysis. The coating was used for the extraction of trifluralin (a common herbicide) and chlorpyrifos from agricultural wastewater and vegetables. Validation resulted in LOQs of 0.45 and 0.50 ug/L, and EFs of 1950 and 2123 for trifluralin and chlorpyrifos, respectively. A good precision was calculated, with RSDs below 11%. Finally, chlorpyrifos was detected in agricultural wastewater (1.2 ug/L) and both analytes were quantified in cucumber (2.4 and 5.6 ug/L for trifluralin and chlorpyrifos, respectively). A magnetic COF nanohybrid (NiFe\({}_{2}\)O\({}_{4}\)@COF) was developed for the SPME extraction of triclosan and methyltricolosan in environmental water and human urine samples [125]. Magnetic NiFe\({}_{2}\)O\({}_{4}\) particles were synthesized by hydrothermal synthesis and the COF was grown in situ under ambient conditions by aldehyde-/amine-based condensation using terephthaladicarboxaldehyde and 1,3,5-tris (4-aminophenyl) benzene. The NiFe\({}_{2}\)O\({}_{4}\)@COF hybrid nanocomposite was physically deposited onto fused silica fibers. The core-shell nanohybrid-based coating was characterized by a pore diameter of 3.9 nm and BET surface (169.7 m\({}^{2}\)/g) larger than those of a pristine COF (1.2 nm and 58.4 m\({}^{2}\)/g, respectively). The extraction selectivity of the NiFe\({}_{2}\)O\({}_{4}\)@COF coating was demonstrated by comparing the EFs of the target analytes with those of five pyrethroid pesticides: EFs of 279 and 334 were calculated for triclosan and methyltricolosan, respectively, whereas values in the 76-147 range were obtained for the other pyrethroids. The adsorption of the analytes was ascribed to hydrophobic and strong \(\pi\)-\(\pi\) interactions between the COF shell and phenyl groups of the OCPs, leading to a higher extraction performance compared to commercially available fibers. The DI-SPME-GC-ECD method exhibited LOQs of 23 and 3.3 ng/L for triclosan and methyltriclosan, respectively, allowing for the detection of the investigated analytes in tap, river, and barrel water samples at the sub-ug/L level. [PERSON] and coworkers developed an ultrastable crystalline, quinoline-linked 2D COF (COF-CN) for the selective extraction of 14 OCPs from environmental water samples [126].