# Applications of Nanomaterial Coatings in Solid-Phase Microextraction (SPME)
## 4 Advances in the Adsorbent Type Used in the Extraction Phase of the SPME Fiber
### Titanium Oxide Nanoparticles as Sorbents for SPME
When designing and synthesizing IONPs for use, their magnetic behavior is crucial, especially in separation technologies where significant magnetization is necessary. Because of their easy surface modification, low cost of synthesis, and nanoscale property manipulation capabilities, iron oxide nanoparticles are widely used in various domains. They are also appropriate for biological applications due to their low toxicity, chemical inertness, and biocompatibility. Also, they are useful tools for environmental cleanup because of their enormous surface area, adaptability, and compatibility with adsorption technologies [79; 80; 81; 82]. Iron oxide nanoparticles can take several forms, such as wustite (FeO), ferrihydrite, goethite, magnetite (Fe\({}_{3}\)O\({}_{4}\)), maghemite (\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)), and hematite (\(\alpha\)-Fe\({}_{2}\)O\({}_{3}\)), depending on their stoichiometry and oxidation state. Magnetite (Fe\({}_{3}\)O\({}_{4}\)) and maghemite (\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)) have been extensively investigated for their distinct crystalline phases. Superparamagnetic iron oxide nanoparticles (SPIONs), particularly Fe\({}_{3}\)O\({}_{4}\), are widely used in a variety of applications due to their ability to exhibit superparamagnetic properties when smaller than 20 nm [83]. Iron oxide nanoparticles and magnetite (FeO\({}_{4}\)) are common magnetic materials used in water treatment because they provide a low-maintenance substitute for conventional adsorbents. FeO\({}_{4}\) nanoparticles are excellent nano-adsorbents for purifying wastewater, especially when functionalized, which improves their catalytic and adsorption capabilities. These nanoparticles are well known for their excellent adsorption capacity, stability, and reusability and can be readily recovered using an external magnetic field [84; 85; 86; 87]. [PERSON] et al. developed a new SPME fiber by embedding FeO\({}_{4}\)/SiO\({}_{2}\) core-shell silica nanoparticles in polypyrrole (PPy) on stainless steel wire. Using direct-immersion (DI-) and headspace (HS)-SPME, this fiber was utilized to extract hexanal and heptanal from urine samples. GC-FID quantification was then performed. SEM and FT-IR were used to characterize the fiber, and important extraction parameters were refined. With detection limits of 0.1 and 0.5 ng/mL for hexanal and heptanal using HS-SPME-GC-FID and 0.1 and 1.0 ng/mL for DI-SPME-GC-FID, the calibration curves demonstrated good linearity (R2 > 0.99). The DI-SPME and HS-SPME replication studies had relative standard deviations of 6.5-6.6% and 5.1-5.3%, respectively. Urine samples without derivatization were successfully treated with both techniques; however, HS-SPME-GC-FID demonstrated better analytical performance and a longer fiber lifetime [88]. For the purpose of magnetic solid-phase extraction (MSPE) of organophosphorus pesticides (OPPs) from juice samples, [PERSON] et al. fabricated a magnetic 3D graphene-iron oxide nanocomposite (3D-G-Fe\({}_{3}\)O\({}_{4}\)). This was followed by gas chromatography-nitrogen phosphorus detection (GC-NPD). Characterization of the 3D-G-FeO\({}_{4}\) was performed with SEM, FT-IR, and VSM. After optimizing key extraction parameters, low detection limits (1.2-5.1 ng/L) and excellent linearity (R2 = 0.9973-0.9999) were obtained. The technique demonstrated good repeatability, with fruit juice OPP recovery rates ranging from 86.6% to 107.5%. GC-MS validation confirmed the findings, showing that the nanocomposite's 3D structure and magnetic characteristics gave it an exceptional extraction capability [40]. Manganese Oxide Nanoparticles as Sorbents for SPME  
Manganese oxide, or MnO, is a common mineral that can be found in a variety of natural settings, including soil, silt, and aquifers. It frequently occurs as discrete particles, gels, or mixtures with other minerals like iron. MnO's special qualities allow it to potentially affect how pollutants behave in the environment through adsorption, photodegradation, and catalytic oxidation [89; 90; 91].