# Magnetic Solid-Phase Extraction of Organic Compounds Based on Graphene Oxide Nanocomposites
## 2 Preparation and Applications of GO for the MSPE of Organic Compounds
### Functionalized Nanocomposites of Magnetic GO with MOFs  
Metal-organic frameworks are mixed organic-inorganic supramolecular materials that became popular in 1995, when [PERSON] and [PERSON] reported the synthesis of a MOF with large rectangular channels [97]. These materials are based on the coordination of metal ions or clusters with bi- or multidentate organic linkers [98; 99]. Metal-organic frameworks exhibit various extraordinary properties including luminosity, tunable pore size, flexibility and thermal stability as well as high surface areas [100; 101]. The combination of graphene oxide and metal organic frameworks enhances the merits of sorbent including its reusability, its pore volume, its dispersion capability, its extraction capacity, its mechanical strength as well as its surface area [102; 103; 104]. [PERSON] et al. developed a sorbent based on magnetic graphene oxide functionalized MOF-199 with the aim to combine the benefits of GO/Fe\({}_{3}\)O\({}_{4}\) and MOFs for the rapid separation and highly selective adsorption of triazole pesticides [105]. The sorbent was employed for the MSPE of triazole pesticides from environmental water samples prior to their determination by HPLC-MS/MS. High adsorption capacity for the target analytes was observed due to the high surface area and pore volume of the novel nanocomposite. A high-affinity graphene oxide-encapsulated magnetic zirconium-MOF was developed for the MSPE of photosensizers hematoporphyrin and hematoporphyrin monomethyl ether from human urine prior to their determination by ultra-performance liquid chromatography-high resolution mass spectrometry (UPLC-HRMS) [106]. The novel sorbent combined the advantages of GO, magnetic nanoparticles with the advantages of large surface area, high porosity, and easy modification of metal-organic frameworks. [PERSON] et al. synthesized magnetic Cu-MOFs embedded within graphene oxide nanocomposites and used it for the MSPE of benzenoid-containing insecticides prior to their determination by HPLC-UV [107]. For this purpose, GO nanosheets were functionalized with silica-coated Fe\({}_{3}\)O\({}_{4}\) nanoparticles with core-shell structured through covalent bonding and subsequently the GO surfaces were modified with Cu-MOFs. The silica shells prevented the oxidation and agglomeration of Fe\({}_{3}\)O\({}_{4}\) nanoparticles and served as a platform to integrate the Fe\({}_{3}\)O\({}_{4}\) particles and GO nanosheets through covalent bonds. Finally, the functionalization with the Cu-MOFs enhanced the extraction efficiency by providing more active sites for adsorption because of the high porosity and tunability of MOFs. Figure 5 shows the SEM images of TEM Cu-MOFs (a) and Fe\({}_{3}\)O\({}_{4}\)@SiO\({}_{2}\)-GO-MOFs (b) as well as the TEM Cu-MOFs (c) and Fe\({}_{3}\)O\({}_{4}\)@SiO\({}_{2}\)-GO-MOFs (d). [PERSON] et al. synthesized a graphene oxide/metal-organic framework-74/Fe\({}_{3}\)O\({}_{4}\)/polytramine (GO/MOF-74/Fe\({}_{3}\)O\({}_{4}\)/PTy) nanoporous composite and used it for the magnetic dispersive micro solid-phase extraction (MD-\(\upmu\)-SPE) of prosthetic drugs prior to their determination with HPLC-UV [102]. The surface modifiers were employed to improve the properties of graphene oxide, including the surface area-to-volume ratio, the adsorption capacity as well as its selectivity. Other nanocomposites of GO and metal-organic frameworks were reported by the working group of [PERSON] [103] and the working group of [PERSON] [104]. The first group synthesized a magnetic zeolitic imidazolate framework (ZIF) 67/graphene oxide composite material and used it for the MSPE of neonicotinoid insecticides from environmental water samples [103]. The combination of the ZIF and GO nanoparticles was performed to facilitate enhancement of the sorbent properties. The second group synthesized a magnetic zeolitic imidazolate framework-7 supported graphene oxide nanocomposite with the assistance of polydopamine and used it for the MSPE of fungicides from environmental water and soil samples.