## 3 Sample Preparation Techniques and Development of Extraction Sorbents
### Solid-Based Extraction
#### 3.2.3 Solid-Phase Extraction (SPE)
This indicates that the method provides merits in terms of reducing the sample size, decreasing organic solvents' consumption, and needing shorter analytical time without affecting the sensitivity of the method. In recent times, miniaturization has become a trend due to various advantages over conventional extraction techniques including shorter extraction time, minimal sample volume, less consumption of organic solvents, and a facile extraction procedure. In 2003, [PERSON] [97] introduced a miniaturised SPE technique termed as dispersive-SPE (dSPE) for the extraction of pesticide residues in produce. Since then, dSPE has become a trend for the preconcentration of various analytes. dSPE involves the dispersion of sorbent material in a sample solution, which greatly increases the surface area in contact. Hence, the extraction efficiency was enhanced substantially. [PERSON] and [PERSON] [98] developed a new method, known as solvent-assisted dSPE, for determination of OPPs. In this method, the dispersion of a sorbent into the aqueous sample maximised the interaction surface between the analytes and the sorbent. Next, centrifugation was carried out and the retained OPPs were dissolved in ethanol. The method exhibited low LOD (0.3 ng mL\({}^{-1}\)) and a pronounced enrichment factor, ranging from 368-376. The developed method offered merits in terms of portability, shorter analysis time, being simple, and minimizing cost. In conclusion, numerous studies have reported on the development of SPE sorbent from various materials. These studies revealed that the extraction efficiency of targeted analytes is greatly influenced by the properties of the sorbent. Therefore, the selection of sorbent material and the physicochemical properties of the targeted analytes should be taken into consideration. Besides that, the findings from the studies suggested that the properties of sorbents can be exploited to enhance trace analytes' preconcentration. Therefore, there is a potential that a multiple ligand sorbent (i.e., bifunctional sorbent) bearing multiple functional moieties such as amino, cyano, and chloro groups can be developed via sol-gel reaction. In the sample preparation field, it would be practical if a single SPE sorbent is capable of simultaneously preconcentrating all OPPs, since OPPs consist of a broad range of polarities and structures. Therefore, the development of functionalised materials as SPE sorbents, focusing on enhancement in selectivity, will continue to progress. Besides that, current research has also been focusing on miniaturization of extraction technique, which could mitigate the weaknesses of the conventional SPE techniques. A new research trend on the advances of SPE has also been noticed. Studies conducted by [PERSON] et al. [99] and [PERSON] [100] introduced the application of sorbent coated on a stainless steel for the enrichment of OPPs and polyaromatic hydrocarbons. A high amount of coating was coated on the meshes, which resulted in the significant increase of surface area in contact. Consequently, this approach shortened the adsorption and desorption process. Besides that, the studies reported low LOD and high recovery of targeted analytes. Therefore, the results indicated that the combination of an improved extraction device and sorbent could result in synergistic effects that greatly improve the extraction efficiency of target analytes. Hence, the approach on enhancing the extraction efficiency via the advancement of SPE device (i.e., cartridge, fruits) is a good strategy, other than focusing on the development of sorbent materials. Table 6 shows the summary of the advantages and limitations of sample preparation techniques for OPPs' determination.