## 3 Sample Preparation Techniques and Development of Extraction Sorbents
### Solid-Based Extraction  
#### 3.2.1 Solid-Phase Microextraction (SPME)  
Solid-phase microextraction (SPME) is an extraction technique introduced by [PERSON] and [PERSON] in 1989 [41]. It has shown tremendous growth as an alternative to other extrac \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Year** & **Technique** & **Analyte** & **Matrix** & **LOD** & **Recovery (\%)** & **Analytical Technique** & **Ref.** \\ \hline
2020 & Nanostructured supramolecular solvent-based LIME & Methyl parathion & Water & 0.27 ng mL\({}^{-1}\) & 92–109.9 & HPLC-UV & [30] \\
2020 & Deep eutectic solvent-based ultrasound-assisted LIME & Phosphalone and chloropyrits & Red grape juice & & & & \\  & & & & & & & \\  & & & & & & & \\
2016 & Miniaturated counter current LLE & Diazinon and malathion & Water & 0.1 ng mL\({}^{-1}\) & 96–110 & GC-FID & [39] \\
2012 & Vortex-assisted LIME & & 12 OPPs & Water and wines & 2-11 ng L\({}^{-1}\) & 70–120 & GC-MS & [31] \\  & & & & & & & \\
2009 & Dispersive liquid-liquid & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\
2007 & Dispersive liquid-liquid & & methyl, fenitathion, chloropyrits & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summary of past studies on the application of LLE as a sample preparation technique for OPPs’ determinations. tion techniques due to its principle as it incorporates sampling, extraction, enrichment, and sample introduction into a single step without solvent. The extraction occurs via sorption of the targeted compound from the sample matrix onto the sorbent coating followed by desorption of the analyte from the coating into an appropriate instrumental system via thermal (headspace-GC) or solvent (HPLC or capillary electrophoretic analysis) [42; 43]. SPME has demonstrated significant impacts in a solvent-free procedure, by which it excludes the use of organic solvents, miniaturization, and automation in the sample preparation field [44]. Besides that, it reduces the analysis time by incorporating sampling, extraction, enrichment, and sample introduction into one step. SPME is also feasible to be combined with various analytical instruments such as gas chromatography (GC), high-performance liquid chromatography (HPLC), and capillary electrophoresis (CE) [45; 46; 47]. Despite the numbers of advantages in comparison to other methods, SPME possesses several disadvantages such as limited sorbent loading, which could affect its sensitivity, fragility, and degradation of the coated fibers, instability of the coating in organic solvent, and time consuming to achieve equilibrium. Another significant disadvantage is a limited number of sorbent coatings available commercially, which, in turn, makes the morphology and chemistry of the coatings restricted [41; 42]. Besides that, the recoveries are generally low as SPME is a non-exhaustive extraction technique [48]. A summary of past studies on the application of SPME as a sample preparation technique for OPPs' determinations is presented in Table 4. [PERSON] et al. [49] developed a method for the preconcentration of OPPs in cows' milk using SPME in headspace mode (HS-SPME) and polydimethylsiloxane/divinylbenzene (PDMS/DVB) as sorbent. The method showed LOD ranging from 2.16-10.85 ng mL\({}^{-1}\) for all the targeted analytes. The recoveries of the developed method that were exhibited were comparable to and even higher than the previous reported studies, except for ethion, due to its high hydrophobicity (Log K\({}_{\text{ow}}\) = 5.07), by which it has higher affinity toward the sample matrix that is richer in lipids than the sorbent [50]. The method is capable of detecting OPPs in cows' milk exposed to OPPs below their limits of quantification. Numerous types of sorbent coatings have been developed to improve extraction efficiency via modification of coating materials. Carbon nanotubes (CNTs), graphene, and metals are commonly used for the modification process [50; 51].