# Exploring the Potential of Microextraction in the Survey of Food Fruits and Vegetable Safety
## 2 Extraction Approaches Used to Assess Food Safety
### Microextraction Approaches  
#### 2.2.1 Sorbent-Based Microextraction Techniques  
Sorbent-based microextraction techniques are based on the SPE principles and mainly include microextraction packed sorbent (MEPS), SPME, and different formats and variations of these approaches [109]. The development of better sorbent coating technology, along with the use of packed sorbents and innovative designs and devices, has enhanced the efficiency and recovery of the target analytes [109; 110]. These techniques use a solid or semi-solid organic polymer as the sorbent immobilized on a substrate to separate and pre-concentrate the analytes, providing simplicity and the possibility of automating the entire process [12; 109]. Sampling and sample preparation can be carried out by headspace extraction or direct immersion extraction. Polymeric sorbents are highly viscous and are prone to irreversibly adsorb matrix interferents. Hence, a sample pre-treatment before the analyte's extraction, such as filtration or centrifugation, is required. After extraction, the desorption can be carried out by applying thermal shock or by exposing it to an organic solvent, followed by chromatographic separation and analysis [109]. Even though sorbent-based extraction techniques cannot handle large sample volumes, they are still valid alternatives to conventional approaches and benefit from the wide range of commercially available fibre phases, as well as stability and reproducibility [12]. SPME, invented by [PERSON] and [PERSON] in 1987 [111], is a solvent-free extraction technique that integrates sampling, extraction, and analyte preconcentration into a single step. It is also characterized by its automation, reliability, and sensitivity [12; 109]. This technique consists of the partitioning of the analytes from the sample solution into the sorbent coating of the SPME fibre, due to intermolecular interaction for the sorbent material [12]. SPME comprises several configurations that improve the high surface-area-to-volume ratio, resulting in smaller extraction periods and higher recoveries [12]. Given that the SPME fibre is retractable inside a syringe needle, it can be directly introduced into a GC inlet or HPLC system via a special interface [109]. Furthermore, this microextraction benefits from the constant development of new sorption coatings. The detection of semi-volatile and non-volatile compounds can be performed in the headspace mode, direct mode, or by membrane extraction (reviewed by [PERSON] et al. [12]). Despite the advantages of SPME over conventional methods, it presents a few limitations mostly related to the sorbent coating technology used in the manufacturing of the SPME fibres. These shortcomings include (i) low operating temperatures; (ii) instability and swelling of the coating if exposed to organic solvents; (iii) SPME fibre short lifetime; and (iv) long extraction equilibrium time due to the slow diffusion of the analyte(s) into viscous sorbents [12]. MEPS is a sample pre-treatment technique based on the miniaturization of SPE, in which the sorbent is integrated into handheld automatic syringes that can control the solvent flow, resulting in low void volumes [12]. In turn, this allows pressure-driven extractions, which are considerably more efficient than conventional SPEs [110; 112]. This technique requires low solvent volumes and shorter sample preparation times and can be applied to smaller samples (volume 10-250 \(\mu\)L) [12; 109]. MEPS comprises sorbent conditioning, sample loading, washing, and analyte elution, with a two-direction flow potential. Hence, this microextraction technique presents enhanced sample-sorbent interaction, sample loading, and improved analyte elution compared to SPE [12]. MEPS can also be performed online, consisting of a fully automatedprocess in which it is possible to use the same syringe for sample extraction and extract injection in the analytical instrumentations [12; 109]. However, when using higher sample volumes, this device often shows limitations.