## 3 Selected Applications of GBMs in Key Miniaturized Techniques
### Pipette-Tip Solid-Phase Extraction and Disposable Pipette Extraction  
Over the years, various forms of miniaturization of conventional SPE have been developed using different devices. PT-SPE is a miniaturized format of SPE, employing a small amount of sorbent packed between two frits or cotton filters within a pipette tip. This tip is then connected to a suitable pipettor or a syringe in more cost-effective setups [13]. Analyte sorption is conducted through sample aspiration and dispensing cycles until partition equilibrium is reached. Generally, the execution of this technique is divided into several steps similar to conventional SPE: (I) conditioning of the sorbent; (II) sorption of analytes (occurring through cycles of aspiration/dispensing); (III) washing of the sorbent to remove sample interferents; (IV) desorption of analytes using an appropriate organic solvent. Advantages over conventional SPE include shorter extraction times, ease of execution, the possibility of on-site extraction, a reduced extraction phase and organic solvent use, and a lower sample volume required [100]. However, since this technique is non-exhaustive, unlike conventional SPE, its performance depends directly on the characteristics of the sorbent used and its specificity for analytes [101]. The unique characteristics of GBMs have led to their successful application in various fields using this technique. For instance, [PERSON] et al. [102] grafted GO nanosheets onto the surface of fibrous silica nanospheres through a water-vapor-induced internal hydrolysis method, aiming at isolating protease inhibitors in yellow catfish, followed by analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Using only 220 mg of the sorbent prepared in a 1 mL pipette tip, the authors achieved LOQs of 0.8-1.6 ng mL\({}^{-1}\), with analyte recoveries above 70% and good reproducibility. These parameters were attributed to the performance of the sorbent produced, which exhibited a highly rough surface after modification with GO, leading to an increased adsorption capacity of the investigated analytes. Furthermore, the sorbent preparation involved a low amount of organic solvents, with aqueous reaction media and renewable washing solvents (water and ethanol). Recently, [PERSON] et al. [103] modified GO sheets with polydopamine for the extraction of alecitinib and its metabolite (M4) in plasma samples using PT-SPE and determination by liquid chromatography with ultraviolet detection (LC-UV). The resulting material exhibited high porosity, increased specific surface area, and was functionalized with functional groups such as amino, hydroxyl, and benzene rings derived from polydopamine. As a consequence, low LOQ values (13.1-16.1 ng mL\({}^{-1}\)), excellent method reproducibility (RSDs \(\leq\) 2.8%), and high analyte recovery rates (>80%) were achieved with just 1 mg of the sorbent packed into the extraction device. The porosity of the material helped to mitigate backpressure issues caused by packing, and the performance of the method results indicated high sorbent selectivity for the target compounds, facilitated by its multiple interaction mechanisms, even in complex biological samples. In a semi-automated approach, [PERSON] et al. [104] packed 10 mg of microwave-assisted synthesized rGO nanosheets into a 200 \(\upmu\)L pipette tip, connecting it to a commercial plastic syringe attached to a dual syringe pump for the extraction of tricolasn from environmental water samples and analysis by HPLC-UV. The authors reported that the primary analyte-sorbent interaction mechanism was the \(\uppi\) bonds of rGO with the aromatic rings of the analyte, resulting in a reproducible method with recoveries exceeding 90%. This method was described as simple, cost-effective, and environmentally friendly, as it only required 1 mL of conditioning solvent and the same amount for desorption and sorbent regeneration, achieving reusability for up to 20 extraction cycles.