## 3 Selected Applications of GBMs in Key Miniaturized Techniques
### Stir Bar Sportive Extraction  
SBSE is a miniaturized technique that emerged in 1999. It is based on using a solid phase employed on a magnetic stirring bar as a device for compound extraction. This technique operates on the principle of partitioning, making it a non-exhaustive technique, in contrast to SPE. The extraction occurs with the exposition of the device containing the extracting phase to the sample medium for a certain period under constant agitation until the partition equilibrium of analytes between the solid and liquid phases is reached. Subsequently, this magnetic bar is exposed to an organic solvent that has an affinity for the compounds adsorbed on the bar, allowing the migration and subsequent injection of this extract into the analytical system [85]. Various coating materials for the bars have been investigated and reported in the literature since its inception, and in the field of graphene derivatives, their applications are diverse [86]. In the environmental field, [PERSON] et al. [87] used a porous nickel foam modified with reduced graphene oxide on its surface (rGO-NF) as a stirring bar for the extraction of six benzotriazole ultraviolet absorbents (BZTs) and their determination by liquid chromatography with a diode array detector (LC-DAD). One of this study's advantages was the extraction device's cost-effective preparation, as the authors reported acquiring the nickel foam commercially, and the hydrothermal reduction of GO occurred in situ on the substrate surface. Additionally, the method demonstrated enrichment factors exceeding 30% for the proposed method, with LODs in the range of 0.33-0.50 \(\upmu\)g L\({}^{-1}\) for the studied compounds. The device could be reused approximately 25 times without a loss in extraction efficiency, showcasing the significant stability of the rGO coating. Another study focused on developing a new coating for stirring bars based on a zirconium dioxide-reduced graphene oxide  
Figure 5: Miniaturized offline sample preparation techniques employing hybrid GBMs. nanocomposite (ZrO\({}_{2}\)-rGO). The authors used the sol-gel methodology to coat the extraction bar made of a magnet encapsulated in glass and its application for the extraction of the organophosphate pesticide ethion in agricultural and river wastewater samples, followed by analysis using negative corona discharge ion mobility spectrometry (NCD-IMS). The method demonstrated a LOD of 1.5 ug L\({}^{-1}\) and recoveries above 90% for the pesticide in actual samples. Furthermore, the ZrO2-rGO-coated bar showed higher sorption efficiency for ethion compared to a bar coated with polydimethylsiloxane (PDMS), attributed to the greater polarity of ZrO\({}_{2}\)+GO, which enhances affinity interactions with the pesticide [88]. Another approach to this method is stir bar sorptive-dispersive microextraction (SBSDME), which combines the advantages of SBSE and d-\(\upmu\)SPE. This method utilizes sorbents based on magnetic nanoparticles that dynamically coat an apparatus containing a bar-shaped magnet. When the device is introduced into the sample at a low stirring speed, the particles remain attached to the magnet, operating like SBSE. As the speed increases, the coating material disperses in the sample due to rotational force. At the end of the procedure, when the rotation stops, the magnetic particles reassemble on the magnet [89]. This methodology is promising for enhancing the pre-concentration process of analytes and reducing factors such as extraction time and the recovery of the sorbent at the end of each extraction. In the context of combining magnetic nanoparticles with GBMs for this method, [PERSON] et al. [90] prepared a magnetic composite consisting of Fe\({}_{3}\)O\({}_{4}\) aggregates grafted onto the surface of rGO for the isolation of seven multiclass pesticides in water samples, followed by HPLC-DAD analysis. The SBSDME method was compared to MSPE.