# 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 GO with Fe\({}_{3}\)O\({}_{4}\) Nanoparticles  
The main disadvantage of graphene oxide-based adsorbents is the important \(\pi\)-\(\pi\) stacking interactions between graphene oxide nanosheets, which are responsible for serious aggregation and restacking of the nanosheets, resulting in a potential block of the active adsorption sites of the sorbent and a decrease of its specific surface area. In order to overcome this problem, functionalization of the sorbent with different molecules that can enter between the GO nanosheet and prevent them from aggregation and restacking can take place [77]. In order to overcome this limitation, [PERSON] et al. developed a magnetic nanodiamond/graphene oxide hybrid and used it for the MSPE of sildenafil from alleged herbal aphrodisiacs by HPLC-DAD system. Functionalization with nanodiamond successfully prevented the aggregation and restacking of GO nanosheets [77]. Functionalization of graphene oxide-based adsorbents can also take place to enhance the extraction efficiency of the material by introducing compatible chemical molecules with high surface area and abundant functional groups in the structure of GO. Polyamidoamine (PAMAM) dendrimer has been used to develop amino-terminated hyper-branched PAMAM polymer grafted magnetic graphene oxide nanosheets for the MSPE of selective serotonin reuptake inhibitors from plasma samples [78]. Due to the large number of terminal groups of polyamidoamine dendrimer, the structural characteristics as well as the internal spaces between their branches, which can trap the target analyte, the functionalized GO/Fe\({}_{3}\)O\({}_{4}\) sorbent exhibited higher extraction efficiency compared to the conventional GO/Fe\({}_{3}\)O\({}_{4}\) nanocomposite. Functionalization with soluble eggshell membrane protein (SEP) was found to increase the stability and adsorption performance as well as accuracy and recoveries of GO/Fe\({}_{3}\)O\({}_{4}\) due to the high density of surface functional groups such as amines, amides and carboxylic groups of SEP [79]. Porphyrin has been also used for the functionalization of GO/Fe\({}_{3}\)O\({}_{4}\) nanocomposite and the sorbent was used for the MSPE of sulfonamides from tap and river water samples [80]. Due to the \(\pi\)-\(\pi\) stacking and electrostatic attraction between the negatively charged functionalized nanocomposite and the positively charged sulfonamides, the extraction process was accelerated. The novel sorbent showed higher adsorption capacity than the conventional GO/Fe\({}_{3}\)O\({}_{4}\). A co-polymer of divinylbenzene (DVB) and glycolylmethylacrylate (GMA) was used for the functionalization of GO/Fe\({}_{3}\)O\({}_{4}\) in order to develop a sorbent for the MSPE of chlorophenols from environmental water prior to their determination by HPLC-MS/MS [81]. Due to \(\pi\)-\(\pi\) stacking and hydrogen-bonding interactions between the analytes and the functionalized adsorbent, good extraction efficiency was observed. Polystyrene (PS) [82] and poly(pyrrole-co-aniline) [83] are two examples of functional groups that were employed to prepare magnetic graphene functionalized nanocomposites, which were used for the MSPE of PAHs from water samples. Polystyrene is rich in phenyl and alkyl groups. Therefore, functionalization with PS enhanced the extraction efficiency by increasing the active surface sites of the material. The sorbent exhibited sufficient surface area, excellent magnetic properties and resulted in good extraction efficiencies and low detection limits [82]. Similarly, the poly(pyrrole-co-aniline) functionalized graphene oxide nanocomposite combined the properties of the polypyrrole and polyaniline co-polymer, the GO, and the magnetic nanoparticles. As a result, the developed nanocomposite exhibited a significant enhancement of extraction efficiency due to the increased number of active surface sites on the sorbent as well as the protection of the Fe\({}_{3}\)O\({}_{4}\) nanoparticles [83].