## 3 Selected Applications of GBMs in Key Miniaturized Techniques
### Magnetic Solid-Phase Extraction  
MSPE is a dispersive extraction technique that resembles the principles of DSPE (and d-\(\upmu\)SPE), differing in the type of sorbent used, which in this case consists of magnetic particles. The sorbent comes into contact with the aqueous sample medium, and through an appropriate agitation rate, the analytes are retained in the magnetic phase. Subsequently, the sorbent is separated by applying an external magnetic force to the vial (usually a magnet) and placed in contact with an organic solvent for the desorption process of the compounds, which is performed by ultrasound or agitation. After this step, the sorbent is separated again, and the extract is collected for instrumental analysis [21]. Since this technique also represents a miniaturization of SPE, several advantages are attributed to MSPE, such as eliminating the need for extraction devices like cartridges or syringes. This elimination helps prevent issues like backpressure and clogging, allowing for the use of particles with different physical characteristics [114]. GBMs in this technique have proven very effective due to their relatively high surface area and capacity for extracting organic molecules. The magnetic nanoparticles most commonly attached to GO/rGO sheets in various studies in the literature are magnetite (Fe\({}_{3}\)O\({}_{4}\)), which are deposited on the surface of these materials through electrostatic interactions [114]. Thus, the applications are diverse, as demonstrated in the study by [PERSON], [PERSON], and [PERSON] [17], where a GO-Fe\({}_{3}\)O\({}_{4}\) nanocomposite was synthesized for the extraction of gingerols from foods, supplements, and ginger-derived beverages using MSPE and analysis by UHPLC-MS/MS. When compared to other sorbents, such as pure GO, GO@SiO\({}_{2}\), or commercial C18 particles, the prepared GO-Fe\({}_{3}\)O\({}_{4}\) sorbent showed equal or superior adsorption capacity for the investigated compounds, standing out for its practicality in being used in the MSPE technique. Consequently, 8 mL of sample was extracted with only 10 mg of the sorbent, resulting in enrichment factors between 9.9 and 30.8 with LOQs of 5 ug L\({}^{-1}\) for the investigated analytes. The reusability of GO-Fe\({}_{3}\)O\({}_{4}\) was determined to be 10 cycles without any loss in extraction efficiency. In another study, [PERSON] and [PERSON] [115] evaluated the performance of two magnetic sorbents: graphene oxide modified with magnetite particles (Fe\({}_{3}\)O\({}_{4}\)@GO) and magnetite anchored on aminopropyl silica particles functionalized with C18 (Fe\({}_{3}\)O\({}_{4}\)@SiO\({}_{2}\)@C18) for the extraction of 33 emerging multiclass contaminants from various groups in wastewater samples, with determination by LC-Orbitrap MS. The authors found that the GO-based sorbent exhibited a better affinity for more polar compounds due to its hydrophilic functional groups, such as hydroxyl and carbonyl. For 19 of the investigated analytes, using 15 mg of Fe\({}_{3}\)O\({}_{4}\)@GO, the method achieved recoveries above 50% for effluent and tap water samples, with LOQs \(\geq\) 1.2 ng L\({}^{-1}\) and a reusability of 10 cycles. Both studies demonstrate the high applicability of magnetically modified GBMs for the clean-up and pre-concentration of organic analytes in complex samples. [PERSON] et al. [116] recently introduced a novel separable sorbent composed of magnetic calcined layered double hydroxide onto graphene oxide (MgO/MgFe\({}_{2}\)O\({}_{4}\)/GO) for efficient extraction of anionic food dyes from water samples, coupled with a straightforward ultraviolet-visible detection (UV-vis) method. In their synthesis, GO and MNPs were amalgamated in methanol as the reaction medium, stirred for 4 h, and dried in an oven at 60 \({}^{\circ}\)C. Characterization assays demonstrated a porous and high-surface material essential for the application in actual samples. The LOD and LOQ for the anionic food dyes ranged from 0.167 to 0.14 mg L\({}^{-1}\) and 0.55 to 0.47 mg L\({}^{-1}\), respectively.