## 5 Conclusions and Future Outlook  
Sample preparation is a critical step in the development of an analytical method for trace analysis, as it influences the sensitivity and extraction efficiency of an analytical method. However, a conventional sample preparation step such as LLE and SPE usually involves high consumption of organic solvents and is tedious and time consuming. Therefore, this led to the emergence of miniaturized sample preparation methods to overcome the drawbacks of the conventional sample preparation methods. This trend could probably be associated with the current trends of the green chemistry approach. Miniaturised extraction techniques such as micro-dispersive solid-phase extraction, magnetic micro solid-phase extraction, liquid-phase microextraction, and vortex-assisted dispersive liquid-liquid microextraction have been receiving huge interest over the past few years. These techniques were developed to minimise organic solvents' consumption, shorten the extraction time, and minimize costs. Next, the analytical performance of a sorbent-based extraction technique is greatly influenced by the selection of sorbent and sorbent synthesis technique. The interaction \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sorbent** & \multicolumn{2}{c}{**Advantages**} & \multicolumn{2}{c}{**Limitations**} & **Ref.** \\ \hline IS & \(\bullet\) & High degree of selectivity & \(\bullet\) & High cost & \\  & & \(\bullet\) & Low stability & [86; 87; 89] \\  & & & \(\bullet\) & Tedious preparation & \\ Graphene & \(\bullet\) & High surface area & \(\bullet\) & Agglomeration of graphene sheets & [75; 87; 88; 92; 93; 94] \\ C\({}_{18}\) & \(\bullet\) & Sensitive towards non-polar compounds & \(\bullet\) & Low recovery for polar compounds & [20; 95] \\ MIP & \(\bullet\) & High selectivity & \(\bullet\) & Limited to compounds with & [76; 81; 85] \\  & \(\bullet\) & Cost effective & & similar structure & \\ Hybrid silica & \(\bullet\) & Porous & \(\bullet\) & Require high purity chemicals & [10; 20; 95; 96] \\  & \(\bullet\) & High surface area & \(\bullet\) & Require high purity chemicals & [10; 20; 95; 96] \\  & \(\bullet\) & Easy to prepare & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Advantages and limitations of sorbent materials used in the extraction of OPPs. between the sorbent, analytes, and sample matrix needs to be considered to ensure good selectivity and extraction efficiency can be achieved. Previous studies reported that neat materials were found to be lacking in extraction efficiency. Therefore, modification of neat sorbent materials with other appropriate materials has become a common practice to alleviate the drawbacks. Modification is achieved via functionalization of a sorbent surface, using numerous materials such as the functionalisation of graphene and multi-walled carbon nanotubes with hydroxyl group, which has improved the sorbent extraction performance and selectivity substantially. In recent times, hybrid materials are becoming a new trend in the development of sorbent materials. Hybrid materials exhibited remarkable improvement in materials' properties and eliminated the disadvantages of neat materials. Numerous studies have reported the remarkable extraction performance of hybrid materials, which have substantially enhanced the selectivity toward target analytes and sensitivity of a developed method. Nevertheless, the sorbent preparation technique is also a crucial factor in determining the properties of a sorbent. Studies have been primarily centered on the functionalisation of sorbent materials via sol-gel technology, as it offers a facile sorbent preparation method with prominent sorbent properties. Sol-gel technique is often used to produce multiple functional ligands' sorbent, which could significantly enhance sorbents' selectivity. For example, amino and cyano moieties can be incorporated onto a single sorbent. The inherent properties make sol-gel technology an outstanding tool to prepare highly selective sorbents.