# Supramolecular Materials as Solid-Phase Microextraction Coatings in Environmental Analysis
## 3 Metal-Organic Frameworks
### MOFs as SPME Coatings for Environmental Applications
#### 3.3.2 Extraction of Polycyclic Aromatic Hydrocarbons
The proposed material was characterized by a higher extraction capability and selectivity than commercially available materials and other developed coatings, with LODs in the 5-42 ng/L range, good linearity, and precision (RSD \(\leq\) 7%). Finally, the method was applied for the analysis of snow, lake and river water, and wastewater samples, detecting a total concentration (\(\Sigma\)) of six PAHs in the 1.47-6.34 ug/L range. Metal azolate frameworks (MAFs) were also tested as SPME coatings by [PERSON] et al. [59] and [PERSON] et al. [60] for the extraction of 7 and 16 PAHs in water, respectively. In both studies, Zn was used as the metal ion and the coatings were obtained by a two-stage methodology consisting of a preliminary step based on the solvothermal synthesis of the MOFs, followed by the dipping of etched SS fibers in a methanolic solution containing the dispersed MOFs. In [PERSON] et al. [59], the synthesis of MAF-66 was performed at room temperature and the layer-by-layer deposition was completed after 10 dipping cycles. The SPME fiber was then used for the HS-SPME-GC-FID analysis of low-molecular-weight PAHs, obtaining LODs in the 0.1-7.5 ng/L range. Two different materials, namely MAF-5 and MAF-6, were tested by [PERSON] et al. [60] for the extraction of the 16 US EPA priority pollutant PAHs from aqueous samples, showing that MAF-6 had the highest extraction capability. Finally, the DI-SPME-high-performance liquid chromatography-fluorescence detection (HPLC-FLD) method was characterized by LOQs at the sub-ug/L level for all the investigated PAHs, except for fluoranthene (LOQ 1.8 ug/L) and benzo(k)fluoranthene (LOQ 1.5 ug/L). [PERSON] et al. developed a HKUST-1-based SPME coating using both the in situ growth and the two-stage process using neutral silicone gel as the adhesive [61]. Both coatings were tested for the HS-SPME-GC-MS analysis of eight PAHs from aqueous samples: the in situ grown coating provided a better extraction capability compared to the two-stage coating due to the pore size and radial alignment of channels. In addition, in situ growth is a less time-consuming procedure. The method was characterized by LOQs in the 0.4-33 ng/L range and proved to be suitable for the extraction of eight PAHs from lake water samples, allowing the detection of medium-weight PAHs in both sites, with concentrations in the 15.3-64.4 ng/L and 19.6-56.9 ng/L range, respectively. [PERSON] et al. tested the extraction capability of a triple-catenated Zn\({}^{2+}\)-pilared MOF, named PUM-210, for the extraction of 16 US EPA PAHs [62]. Compared to the commonly applied homopletic materials, this framework incorporates two different ligands, i.e., 2,6-naphthalenedicarboxylic acid and a pyridine-functionalized biphenylene ligand, for the complexation of Zn(II) ions. The MOF was obtained by solvothermal synthesis and the coating was deposited onto a silica fiber by means of epoxy glue. The developed coating provided low quantitation limits, in the 1-7 ng/L range, and very high enhancement factors in the 300-14,950 range. Finally, the addition of BTEX as interfering compounds did not affect the quantitation of PAHs due to the presence of additional \(\pi\)-\(\pi\) interactions, higher hydrophobicity, and size complementarity between the MOF and the analytes. [PERSON] et al. developed a sheathed MOF-based SPME coating through the in situ heteroepitaxial growth of copper-2,5-diaminoterephthalate crystals (Cu-DAT) on copper wires, followed by dip-coating to obtain a PI sheath [63]. The coating was deposited by a multi-step synthesis directly onto the copper wire (Figure 4): (A) copper hydroxide nanotubes were grown onto the fiber to provide a substrate for the in situ growth of the MOF; (B) the fiber was immersed in the ligand solution; (C) the material was annealed; and (D) the PI sheath coating was obtained by dip-coating.