# Supramolecular Materials as Solid-Phase Microextraction Coatings in Environmental Analysis
## 4 Covalent Organic Frameworks (COFs)
### COFs as SPME Coatings for Environmental Applications
#### 4.3.1 Extraction of Polycyclic Aromatic Hydrocarbons and Nitroaromatic Compounds
When applied to the analysis of contaminated soil samples, both BTEX and PAHs were quantified at sub-trace levels, in the 0.26-3.6 ug/g and 0.02-1.8 ng/g ranges, respectively. As for the DI-SPME extraction of PAHs from aqueous samples, novel COF-based coatings have been proposed [102; 103; 104; 101; 111; 112]. [PERSON] and coworkers synthesized by ultrasonic-assisted reaction a COF based on 1,3,5-triformylphloroglucinol (Tp) and benzidine (BD), which was grafted on etched SS fibers using APTES [111]. The electroetching procedure resulted in an array of nanopores on the SS surface, promoting the grafting of the COF in the microwells. The SPME fibers were tested for the extraction of seven model PAHs from tap and lake water samples followed by GC-FID analysis. Validation resulted in LODs in the 1-5 ug/L range, RSDs! 10%, and recoveries in the 88-163% range. [PERSON] et al. developed a triazine-based COF under solvothermal conditions, subsequently deposited onto SS wires using an epoxy resin. Finally, the SS wires were inserted in a peek tube to be used for the IT-SPME-LC-UV determination of different contaminants in environmental water samples [112]. The good extraction capability towards eight model PAHs, four estrogens, and eight plasticizers was assessed by achieving EFs in the 542-942, 190-929, and 68-1235 ranges, respectively. After optimization of the extraction conditions, the IT-SPME-LC-UV method was validated for the analysis of PAHs, obtaining LOQs in the 13-33 ng/L range, a fiber-to fiber reproducibility with RSDs! 14%, and a wide linear range. The method was then applied for the analysis of tap, river, and rainwater samples; however, no analyte could be detected in unspiked samples. In another study, COF TpPa-1 was used as a template framework to develop a novel carbonaceous material [102]: the derived N-doped porous carbons (TpPa-1-1000) were deposited onto SS wires by physical deposition and used for the extraction of PAHs from soil samples. The TpPa-1-1000 material featured a high nitrogen content (5.62% atomic), a specific surface area of 435.6 m\({}^{2}\)/g, a uniform pore size distribution (3.9 nm), and a porous layered structure, thus increasing the number of accessible binding sites for promoting the interaction of the adsorbent with the target analytes. Compared to commercially available materials, the coating provided enhanced EFs (in the 1686-41,294 range) due to both the high degree of graphitization and the formation of electron-donor-acceptor interactions. The validation of the DI-SPME-GC-MS method resulted in LOQs in the range of 10.4-28.5 \(\upmu\)g/kg of soil sample, and RSDs lower than 12%. A DI-SPME-GC-MS method was also proposed by [PERSON] and coworkers, who tested three different COF-modified graphitic carbon nitride (g-C\({}_{3}\)N\({}_{4}\)) materials for the extraction of PAHs from aqueous samples [103]. The g-C\({}_{3}\)N\({}_{4}\)@TpBD coating provided the best extraction performances toward the investigated PAHs. The developed coating was characterized by higher extraction performances than commercial 85 \(\upmu\)m PA, 60 \(\upmu\)m PDMS/DVB, and 100 \(\upmu\)m PDMS fibers, probably due to the \(\uppi\)-conjugated structure of g-C\({}_{3}\)N\({}_{4}\), allowing for \(\uppi\)-\(\uppi\) stacking and hydrophobic and electrostatic interaction with the target analytes. The DI-SPME-GC-MS method showed LOQs in the 0.07-0.17 \(\upmu\)g/L range, good linearity (over a three orders of magnitude range), and RSDs always lower than 11%. Finally, the method was applied for the analysis of river, lake, well, and rainwater samples and melted snow, allowing the detection of naphthalene and acenaphthene at the sub-\(\upmu\)g/L level. A multi-component coating was developed by [PERSON] and coworkers: carbon fibers were coated with titania nanorod arrays (NARs) and functionalized with either biochar nanospheres or COF nanospheres [104]. The obtained hybrid fibers were introduced in a PEEK tube to be used for the IT-SPME extraction of PAHs before LC-UV analysis.