## 3 Sample Preparation Techniques and Development of Extraction Sorbents
### Solid-Based Extraction
#### 3.2.2 Stir-Bar Sportive Extraction (SBSE)
Next, OH-functionalized multiwalled carbon nanotubes (OH-MWCNTs) were prepared by [PERSON] and [PERSON] [65] as SBSE stir-bar coating for OPPs' extraction from water samples coupled with GC-MS. Previously, they had prepared MWCNTs as SBSE coating material for OPPs' and polycyclic aromatic hydrocarbons' (PAHs) determination. However, there were several drawbacks such as coating instability and lacking in sensitivity [67]. This could have been due to insolubility of CNTs in organic and aqueous solvents, which restricts its usage in a sol-gel preparation. Therefore, OH-MWCNTs were used to enhance CNTs' dispersion in a sol-gel system. The OH-MWCNTs were selected as they enhance CNTs' solubility and generate stable structure, as this polymer binds the MWCNTs' stationary phase to the growing silica network during polycondensation process [65; 68]. The developed method employing the OH-MWCNTs' sorbent and GC-MS showed low LOD (5-10 ng L\({}^{-1}\)) and satisfactory RSD (7.2-12.4%). These results showed the sensitivity and validity of the method for the extraction of OPPs in water samples. Nevertheless, the method showed adequate recovery for the targeted analytes, ranging from 67-84%. This indicated that the method was lacking in accuracy. [PERSON] et al. [64] developed zirconium dioxide-reduced graphene oxide (ZrO\({}_{2}\)-rGO) as a new coating for SBSE. The ZrO\({}_{2}\)-rGO sorbent coating was used for enrichment of ethion from water samples prior to NCD-IMS analysis. The LOD of the method was 1.5 ng mL\({}^{-1}\) with good RSD (6%). Besides that, high recovery was also obtained, ranging from 93-97%, indicating the accuracy of the developed method. The good analytical performance was possibly due to a high surface area of graphene and good sensitivity of ZrO\({}_{2}\) toward phosphate groups in ethion, which promoted better extraction efficiency. The applicability of SBSE was further improved and extended into microextraction following the trend of method miniaturization. [PERSON] et al. [69] introduced a new method, known as stir-bar sorptive-dispersive microextraction (SBSD\(\upmu\)E). This method incorporates the principles of two extraction methods, namely, stir-bar sorptive extraction (SBSE) and dispersive solid-phase microextraction based on magnetic nanoparticles (d-\(\upmu\)SPE). In SBSD\(\upmu\)E method, magnetic nanoparticles (MNPs) were coated on a magnetic stir bar. At a low stirring rate, the technique acts as SBSE, while at a high stirring rate, dispersion of MNPs into a sample solution (or desorbing solvent) took place. The MNPs return to the magnetic bar once the stirring process ended. Therefore, [PERSON] et al. [70] developed a SBSD\(\upmu\)E method with magnetically modified graphene (G-Fe\({}_{3}\)O\({}_{4}\)) for the preconcentration of seven different classes of pesticides from water samples coupled with HPLC. The performance of the developed method was compared with magnetic solid-phase extraction (MSPE). Comparable recoveries of targeted analytes were achieved, ranging from 20-75% and 22-82% for SBSD\(\upmu\)E and MSPE, respectively. However, the developed SBSDuE method offers a rapid extraction process and easy separation of sorbent from the sample solution. The method could also provide a high enrichment factor due to effective mixing of a large volume of samples, hence, improving the LOD. Based on Table 3, the SBSE methods obtained satisfactory extraction recoveries despite the low LODs. Thus, further improvement and development should be carried out to improve their extraction performances in terms of coating material and technical aspect. However, previous studies concentrated on the modification of coating material and only limited studies reported on the improvement of structural modification of stir-bar devices [71]. Therefore, more studies should be carried out on enhancing stir-bar devices and automation of SBSE.