## 3 Sample Preparation Techniques and Development of Extraction Sorbents
### Solid-Based Extraction
#### 3.2.3 Solid-Phase Extraction (SPE)
Hence, the selectivity of MIPs has initiated the extensive use of MIPs as SPE selective sorbent for determination of OPPs, as eloquently stated by [PERSON] et al. [82]. Besides that, MIP-based sorbents are also stable with organic solvents, extreme pH, and high temperatures [76]. However, MIPs' primary drawback is their incapability to simultaneously extract huge number of OPPs due to the wide range of structures and polarities. Hence, different sorbents need to be developed for different analytes [80]. A solid-phase extraction-capillary electrophoresis (SPE-CE) method was developed by [PERSON] et al. [83] using MIP (trichloron as template) for the extraction of trichloron from cucumber, lettuce, and radish samples. The LOD of the developed method was 4.9 ng g\({}^{-1}\) with satisfactory recovery ranging from 77.6-93.2%. It was noted that the method is lacking in sensitivity, as indicated by the high value of LOD in comparison to other methods. This probably is due to the use of CE, as its main limitation is sensitivity of detection, owing to its small inner diameter of the capillary (50-75 \(\upmu\)m) [12]. The lack in sensitivity of MIP-SPE sorbents initiated attempts to improve the sensitivity by combining MIPs with other materials. [PERSON] et al. [84] prepared a new SPE sorbent from a combination of MIP and restricted access material (RAM). Malathion was used as a template molecule and glycolimetachrylate (GMA) as a pro-hydrophilic co-monomer for determination of six selected OPPs from honey samples prior to quantification by GC-FPD. MIPs are best known for their high selectivity due to specific recognition capability for targeted analytes. However, MIPs are incapable of eliminating macromolecules such as proteins and lipids simultaneously. This is due to strong adsorption of the macromolecules to the MIPs' surfaces via hydrophobic interaction, which affects the recognition properties of MIPs [85]. RAM is a porous support, which is capable of eliminating macromolecules based on the size-exclusion mechanism [86]. Therefore, it is interesting to combine MIPs and RAM for selective enrichment of targeted OPPs. The developed method showed low LOD for all the selected OPPs, ranging from 0.5-1.9 ng mL\({}^{-1}\) with excellent RSD (2.25-5.12%). Comparison was carried out with several sorbents, namely, MSPE, C\({}_{18}\), and Florisil in terms of extraction recovery to determine the applicability of the developed method for honey samples. Results showed that the RAM-MISPE method exhibited high extraction efficiency (90.9-97.6%) in comparison to MISPE (90.5-96.2%), C\({}_{18}\) SPE (80.1-85.9%), and Florisil SPE (72.3-77.4%), respectively. The developed method obtained high recovery due to its high selectivity toward the OPPs and good restricted access function. The good performance of the method is also probably due to the use of GC-FPD as a detection system, which is selective toward compounds containing sulfur and phosphorus such as OPPs. There was a minute difference in the extraction recovery between RAM-MISPE and MISPE, which was only 1%. The extraction recovery of C\({}_{18}\) SPE and Florisil SPE were slightly lower in comparison to RAM-MISPE and MISPE, which were probably due to lack of affinities and non-specific recognition toward the analytes. In addition, the analytical time was significantly reduced, as the sample pre-treatment procedure for honey prior to extraction was omitted. Over the past few years, attention has been primarily focused on the development of selective sorbent material for SPE. Immunosorbents (IS), also known as immunoaffinity extraction, has been introduced to cater to the need of selective support in sample preparation, which is based on the antigen-antibody interactions. Immunosorbents are synthesized by linking the antibodies to solid support. IS are highly specific for a particular analyte. However, they can also bind with structurally similar analytes, known as the cross reactivity of antibody [87].