# Supramolecular Materials as Solid-Phase Microextraction Coatings in Environmental Analysis
## 3 Metal-Organic Frameworks
### MOFs as SPME Coatings for Environmental Applications
#### 3.3.7 Extraction of Other Compound Classes  
A hollow zirconium-porphyrin-based MOF (HZ-PMOF) was proposed as an SPME coating for the extraction of 1-naphthol and 2-naphthol, which are extremely toxic environmental contaminants, widely used in industry as precursors for the production of dyes, pesticides, and pharmaceuticals [85]. The MOF was synthetized by a solvothermal approach and physically deposited by means of a polyimide sealing resin. Comparing the non-hollow with the hollow MOF material, different morphologies were obtained: the HZ-PMOF exhibited mesopores and a BET surface of 1585 m\({}^{2}\)/g, with benefits in terms of mass transfer efficiency and specific surface area, whereas the non-hollow material was characterized only by micropores and a surface of 997 m\({}^{2}\)/g. The developed HS-SPME-GC-MS/MS method based on the HZ-PMOF-coated fiber was validated, obtaining low LODs (1.0 ng/L) for both naphthols and, applied to the analysis of environmental water samples from five cities in China, detecting the analytes in two out of five samples (37.7 \(\pm\) 5.6 and 15.0 \(\pm\) 3.4 ng/L for 1- naphthol and 48.9 \(\pm\) 4.3 and 8.9 \(\pm\) 2.1 ng/L for 2- naphthol, respectively). [PERSON] and [PERSON] developed a PPy/chromium-based MOF nanocomposite, PPy@MIL-101(Cr), which was obtained by the hydrothermal method and deposited by electrochemical polymerization of pyrrole onto SS wires [86]. The coating was tested for the extraction from soil samples of methyl tert-butyl ether, a persistent environmental contaminant used as an octane enhancer in gasoline [87]. The novel material showed a higher extraction capability than commercially available materials and pure electrodeposited PPy due to the larger sorptive surface area and stronger interactions. The validation of the HS-SPME-GC-FID method demonstrated a LOQ value of 0.5 ng/g and a linear response over four orders of magnitude. As a main drawback, a low intra-fiber reproducibility was observed, with RSDs up to 26% due to the scarce robustness of the electropolymerization process. Finally, the validated method was applied for the quantitation of methyl tert-butyleither in six soil samples collected from an oil refining company and different gas stations, detecting the analyte in the 0.92(\(\pm\)0.48)-2.72(\(\pm\)0.50) \(\mathrm{\SIUnitSymbolMicro g}\) range. In 2019, [PERSON] et al. developed a porous carbon SPME coating performing both hydrothermal growth of MOF-74 and in situ carbonization on SS wires [88]. The MOF-74-C coating was tested for the extraction of five odorous organic contaminants, namely, 2-chlorophenol, 2,4,6-trichloroanisole, 2-isobutyl-3-methoxypyrazine, thiophenol, and 4-methylthiophenol from water samples. The developed material showed an extraction efficiency 2.0-16.0 times higher than PDMS and PA fibers, whereas similar results were obtained using the PDMS-DVB fiber. Compared to the commercial polymeric materials, the MOF-74C coating was characterized by enhanced selectivity due to the presence of micropores with sizes ranging from 0.59 to 1.71 nm, very close to the dynamic diameters of the odorants, thus resulting in a sieve and micropore-filling effect. The DI-SPME-GC-MS method was validated, obtaining LOQs in the 0.03-300 \(\mathrm{ng/L}\) range, a three-to-five order of magnitude linear range, recoveries in the 90.1-107.3% range, and RDSs always lower than 8.8%. The method was finally applied to the analysis of wastewater, tap, and river water samples, detecting 2-isobutyl-3-methoxypyrazine in the surface water sample at trace levels (0.2 \(\mathrm{ng/L}\)). UiO-66-NH\({}_{2}\) can be considered as an excellent MOF platform to obtain hybrid materials [89; 90; 91]. In 2019, [PERSON] et al. developed zirconium and nitrogen co-doped ordered mesoporous carbon (Zr/N-OMC) SPME coatings to be used for the extraction of substituted phenolic compounds [89].