## 3 Sample Preparation Techniques and Development of Extraction Sorbents
### Solid-Based Extraction
#### 3.2.3 Solid-Phase Extraction (SPE)
The sorbent demonstrated good stability and regeneration by which it could be regenerated 25 times without a significant decrease in extraction efficiency. As such, this study provides an additional insight into the potential to explore more hybrid materials prepared via sol-gel reaction for application in analytical extraction. Consequently, this study has prompted a trend in development of SPE sorbent using a sol-gel technique. Several studies have reported the development of silica-based SPE sorbent using a sol-gel technique for OPPs' determination [10; 20; 95]. A hybrid silica-based SPE sorbent methyltrimethoxysilane-cyanopropyltriethoxysilane (MTMOS-CNPrTEOS) was prepared by [PERSON] et al. [95] via sol-gel technique for simultaneous extraction of polar (dicrotophos and methanolophos) and non-polar (diazmon, malathion, methidathion, and chlorpyrifos) OPPs from tap water and lake water samples prior to quantification using GC-MS. A commercial C\({}_{18}\) SPE sorbent was used for comparison purpose. Resultsindicated that the developed method exhibited a low LOD (0.01-0.02 ng mL\({}^{-1}\)), which was 5-10\(\times\) lower than the MRL set by the European Union (EU) for water samples. The LOD of the developed method was 5-8\(\times\) lower in comparison to the LOD of C\({}_{18}\) sorbent. The SPE-MTMOS-CNPrTEOS-GC-MS method showed good recovery, ranging from 84-99%, and excellent precision (0.06-6.5%). The remarkable results of the developed method could probably be due to the hybrid sorbent possessing high surface area (585 m\({}^{2}\) g\({}^{-1}\)) and porous structure, which promotes the extraction efficiency. The sol-gel hybrid MTMOS-CNPrTEOS showed high selectivity toward the polar analytes compared to the non-polar analytes. These findings showed that the introduction of CNPrTEOS to MTMOS improved the hydrophilicity of the sorbent and promoted the interaction of both polar and non-polar OPPs with the developed sorbent. Magnetic nanoparticles (MNPs) and graphene were introduced in combination with silica-based materials via sol-gel technology to improve ease of separation, sorbent surface area, and enhancement of sorbent ability for simultaneous enrichment of polar and non-polar analytes. A study carried out by [PERSON] et al. [10] successfully prepared magnetic nanoparticles' graphene-based cyanopropyltriethoxysilane (Fe\({}_{3}\)O\({}_{4}\)@C-CNPrTEOS). The sorbent material showed efficient OPPs' extraction from fresh cows' milk samples with minimal sample preparation, by which it only involved simple dilution and omitted acid treatment for fat and protein matrix elimination. A gas chromatography micro-electron capture detector (GC-uECD) was employed as a detection system. The sorbent exhibited high tolerance to matrix interferences and good reusability (10 adsorption-elution cycles). It also showed high enrichment factors (2400) and sensitivity (0.01-0.6 ng mL\({}^{-1}\)). The developed method provided good recovery (82-94%), probably due to graphene hydrophobic properties and the presence of polar cyanopropyl moieties (-C\(\equiv\)N) from CNPrTEOS that enabled simultaneous preconcentration of polar and non-polar OPPs. Therefore, this study revealed that the fabrication of graphene- and silica-based materials shows excellent preconcentration of trace analytes from complex matrix. [PERSON] and [PERSON] [96] developed a SPE method using sol-gel hybrid MTMOS-CPTES for the preconcentration of three selected OPPs, namely, chlorpyrifos, profenofos, and malathion from red apple and purple grape samples prior to GC-MS analysis. The developed SPE-MTMOS CPTES-GC-MS method achieved good LODs, ranging from 0.01-0.07 ug mL\({}^{-1}\), with good recoveries (88.33-120.7%) for all the targeted analytes. The method used a low sample volume (1 mL) and eluent volume (1 mL) but the developed method was capable of providing a good detection limit.