# Supramolecular Materials as Solid-Phase Microextraction Coatings in Environmental Analysis
## 4 Covalent Organic Frameworks (COFs)
### COFs as SPME Coatings for Environmental Applications
#### 4.3.6 Extraction of Other Compound Classes by COF-Based SPME  
Phthalic acid esters (PAEs) are a class of plasticizers widely used in the polymer industry. Different compounds have been included in the list of priority substances by the US EPA due to the potential endocrine-disrupting activity; therefore, the development of new analytical methods able to detect these compounds at trace levels in environmental and biological matrices is demanded [134; 135]. To improve their enrichment and selective extraction, [PERSON] and coworkers developed different \(\beta\)-keto-beamamine-linked COF coatings [96]. Four different COFs were tested, all synthesized by MC to obtain a clay-like material that was deposited onto APTES-pretreated SS fibers, obtaining covalently bonded COF coatings. The best performance was obtained using Tp and 4,4\({}^{\prime}\)-diamino-p-terphenyl (TpTh-COF). The material showed high hydrophobicity, a BET surface of 267.6 m\({}^{2}\)/g, and an average pore diameter of 2.52 nm. The analytes could be adsorbed via hydrogen bonding, \(\pi\)-\(\pi\) and hydrophobic interactions, together with a size-matching effect to guarantee a good extraction selectivity. The DI-SPME-GC-MS/MS method was validated, obtaining LOQs in the 0.2-0.5 ng/L range, EFs in the 1140-3720 range, and RSDs always lower than 10%. The analysis of environmental samples resulted in the detection of dipently phthalate (0.27 ng/L) and butyl benzyl phthalate (11.62 ng/L), disohexyl phthalate (0.33 ng/L), dipently phthalate (1.65 ng/L), and butyl benzyl phthalate (2.34 ng/L) in lake water. Porphyrin-based COFs were proposed as novel materials to be used for the EE-SPME extraction of PAEs [136]: the coating was obtained by in situ electropolymerization onto etched SS fibers, obtaining a fine tuning for both the thickness and morphology of the coating. The final COF exhibited a good crystallinity, with stacked 2D-COF sheets, and good conductivity due to the conjugated macrocycle of the porphyrin ligand. The use of EE-SPME resulted in improved selectivity towards PAEs, even in the presence of interfering compounds, including vitamin C, bovine serum albumin, hemoglobin, aromatic amines, PAHs, and hydroxyl-PAHs. The application of a constant positive voltage increased the extraction of negatively charged PAEs while oxidizing hydroxyl-PAHs to aldehydes. The \(\pi\)-\(\pi\) stacking of porphyrin between the 2D adjacent layers produced a high value of charge carrier mobility, thus improving the extraction capability, whereas the amino groups interacted with the analytes by hydrogen bonding. The EE-SPME-GC-MS method was validated for six model PAEs, obtaining LOQs in the 0.2-10 ng/L range and RSDs \(\leq\) 7%. When applied to the analysis of environmental water samples, diisobutyl phthalate, di-n-butyl phthalate, and dihexyl phthalate were detected in lake water in the 45.9-208.6 ng/L range, whereas di-n-butyl phthalate and dihexyl phthalate were detected in the 40.6-178.7 ng/L range in industrial wastewater samples. [PERSON] and coworkers tested the extraction capability of TpPa-1 for the extraction of synthetic musks from water samples [137]. These compounds are contaminants of emerging concern due to their extensive use, persistence, and bioaccumulation, leading to their widespread presence in environmental and biological matrices. The novel COF coating was synthesized using the solvothermal approach and deposited onto etched SS wires using silicone glue. The material was tested for the DI-SPME-GC-MS/MS analysis of six model synthetic musks, obtaining EFs in the 1214-12,487 range, higher than those achieved using commercial fibers due to hydrophobic interactions and \(\pi\)-\(\pi\) stacking. After validation, LOQs in the 0.04-0.31 ng/L range and RSDs \(<\) 10% were obtained. Finally, the DI-SPME-GC-MS/MS was applied for the analysis of tap, underground, and river water, determining contamination levels from 0.72 to 571.1 ng/L.