# Supramolecular Materials as Solid-Phase Microextraction Coatings in Environmental Analysis
## 4 Covalent Organic Frameworks (COFs)
### COFs as SPME Coatings for Environmental Applications
#### 4.3.2 Extraction of Phenols and Derivatives
The reliability of the method for the determination of the investigated analytes was attested at trace level, obtaining LOQs in the 1.3-2.4 ng/L range with RSDs \(<\) 8%. The feasibility of the method was further demonstrated by analyzing water and soil certified reference materials, obtaining phenol concentrations in compliance with the reference value. Finally, [PERSON] and coworkers developed a COF-graphene oxide composite material (COF-GO) deposited onto a glass fiber using a silicone sealant to be used as an SPME coating for the analysis of bisphenol A [97], a well-recognized endocrine-disrupting compound used in the polymer and packaging industries. The hybrid material was synthesized by a three-step synthesis involving: (i) the preparation of the amino-functionalized GO using APTES, (ii) the addition of Tp between the layers of the material, and (iii) the in situ growth of the COF. The functionalization of GO with the COF increased the BET surface, pore volume, and the interlayer spacing from 353 m\({}^{2}\)/g, 0.16 g/cm\({}^{3}\) and 8.4 A to 824 m\({}^{2}\)/g, 0.46 g/cm\({}^{3}\), and 14.7 A, respectively, thus providing more active sites and faster mass transfer processes. The obtained SPME fibers were used for the CFDI-MS determination of bisphenol A in water samples, obtaining an extraction performance 2.2-4.7 times higher than TpBD and GO and 2.1-4.9-fold higher than 65 um PDMS/DVB-, 85 um PA-, and 100 um PDMS-coated fibers. The validation of the DI-SPME-CFDI-MS method resulted in LOD and LOQ values at sub-trace levels (22.2 and 73.9 ng/L, respectively) and RSDs \(<\) 6%. When applied to the analysis of river and seawater samples, bisphenol A was detected in all samples in the 0.1222(\(\pm\)0.0077)-4.794(\(\pm\)0.072) range, with recovery rates in the 95-107% range. The same research group developed different COF-based coatings for the analysis of tetrabromobisphenol A (TBBPA) and its analogs in environmental matrices using ambient mass spectrometry [98; 119; 120]. These pollutants have gained great attention due to their worldwide distribution, persistence, bioaccumulation, immunotoxicity, and neurotoxicity. TpBD-COF and multicomponent COFs were tested for the extraction of TBBPA and its analogs from environmental water samples. In an early study, a TpBD-COF was tested as an SPME coating for the DI-SPME-constant flow desorption ionization-mass spectrometry (CFDI-MS) analysis of TBBPA in water samples, obtaining LOD and LOQ values of 0.92 and 3.1 ng/L [119]. To improve the extraction performance of the SPME, different multi-component COFs containing Tp, Pa, and BD were tested for the analysis of TBBPA derivatives in water samples. The main feature of the multicomponent COF is the pore size tunability by changing the ratio of the organic linkers: the best performance was obtained using the TpPaBD\({}_{50}\) framework, exhibiting extraction efficiencies up to four times higher than TpPa and TpBD COFs [120]. A further study demonstrated that the best analytical performance could be obtained using porous TpBD, synthesized using a polystyrene sphere (PS) template-assisted method (Figure 8) [98]. Porous TpBD was characterized by a hierarchical porous structure with a BET surface and pore volume higher than those of the conventional TpBD (797 m\({}^{2}\)/g and 0.75 cm\({}^{3}\)/g vs. 638 m\({}^{2}\)/g and 0.41 cm\({}^{3}\)/g). The extraction capabilities of the COF were strongly related to its hierarchical porous structure, which featured micro-, meso-, and macropores, promoting the diffusion/mass transfer pro cesses. The CFDI-MS-based method for the analysis of four TBBPA analogs showed good performance, with LOQs in the 0.4-3.2 ng/L range and good precision, with RSDs < 8%. When applied to the analysis of environmental samples, contamination was assessed for all the river water samples, with a concentration up to 51 ng/L and, for two out of three seawater samples, concentration levels up to 66 ng/L.