# 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
Manganese dioxide nanoparticles (MnO\({}_{2}\) NPs) have a vast surface area, strong oxidizing and adsorptive properties, and durability even in acidic environments. MnO\({}_{2}\) NPs are well known for their ability to effectively remove organic contaminants and heavy metals from water. They can be effectively separated using an external magnetic field because they are frequently boosted by magnetic compounds. These nanoparticles' chemical and physical interactions with polymers make them popular for removing dyes, and their supermagnetic characteristics make the separation process easier at ambient temperature. Through adsorption, ion exchange, and coprecipitation, MnO\({}_{2}\) also efficiently eliminates heavy metal ions [92; 93]. [PERSON] and [PERSON]'s study involved the electrospinning of manganese oxide (MnO) nanoparticles into a nanofibrous polycaprolactone (polyamide 6, PA6) coating. This coating was used as a novel fiber coating for the HS-SPME of specific phthalate esters (PEs) in water samples before GC-\(\upmu\)CCD analysis. Thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, and SEM were used to characterize the coating. Important factors that affect the effectiveness of HS-SPME were optimized, such as extraction temperature, ionic strength, and extraction/desorption periods. The technique demonstrated a linear dynamic range of 0.500-500 ng/mL, limits of detection ranging from 0.0400 to 0.193 ng/mL, and relative standard deviations between 1.86% and 10.9% under these circumstances. The technique obtained relative recoveries of 90.3% to 107% when used on actual water samples, such as soda, river water, bottled water, and mineral water, proving its efficacy in identifying phthalate esters in a range of aqueous matrices [94]. [PERSON] and [PERSON] once more investigated the extraction and identification of carcinogenic nitrophenols (NPs), whereby contamination of soil and water poses serious health dangers. Using electrospinning, they created polyurethane-manganese oxide (PU-MnO) composite nanofibers and showed how effective they were in extracting monotrophenols. Gas chromatography-microelectron capture detection (GC-\(\upmu\)CCD) in conjunction with a green HS-SPME technique used these nanofibers as adsorbents. The researchers obtained a linear dynamic range of 0.100-500 ng/mL, relative standard deviations (RSDs) of 2.53-11.2% (\(n=3\)), and limits of detection of 0.0201 and 0.138 ng/mL after optimizing critical extraction parameters. Relative recoveries for river and wastewater samples using this approach ranged from 90.3% to 105%. The efficiency of the environmentally friendly analytical technique and PU-MnO nanofibers for identifying mono-nitrophenols in actual water samples was validated by the investigation [95]. Zinc Oxide Nanoparticles as Sorbents for SPME  
The distinct electrical and optical characteristics of one-dimensional (1D) ZnO nanostructures, which result from their size and dimensionality, make them highly desirable. They are useful for basic research and as useful parts of nanodevices because of these characteristics. Their employment as interconnectors is also made possible by their 1D shape. Applications of 1D ZnO nanostructures demonstrate their versatility and promise in cutting-edge technologies, including field-emission devices, gas sensors, UV photodetectors, solar cells, light-emitting diodes, and nanolasers [96; 97]. More importantly, ZnO nanoparticles (NPs) are less expensive and easier to create than other nanomaterials. They can also be deposited on a wide range of substrates with precise and perfectly aligned orientations [98]. Also, all of these properties make them a good candidate in SPME fiber applications. [PERSON] et al. studied the utilization of zinc oxide (ZnO)-coated glass fibers for assessing trihalomethanes (THMs) by HS-SPME-GC. Energy-dispersive X-ray spectroscopy and scanning electron microscopy were used to characterize the homogenous and porous ZnO layer that was applied on LiO-ZrO\({}_{2}\)-BaO-SiO\({}_{2}\) glass fibers.