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Berenguer, C.V.; García-Cansino, L.; García, M.�.; Marina, M.L.; Câmara, J.S.; Pereira, J.A.M. Microextraction Approaches Used to Assess Food Safety. Encyclopedia. Available online: (accessed on 15 June 2024).
Berenguer CV, García-Cansino L, García M�, Marina ML, Câmara JS, Pereira JAM. Microextraction Approaches Used to Assess Food Safety. Encyclopedia. Available at: Accessed June 15, 2024.
Berenguer, Cristina V., Laura García-Cansino, María Ángeles García, María Luisa Marina, José S. Câmara, Jorge A. M. Pereira. "Microextraction Approaches Used to Assess Food Safety" Encyclopedia, (accessed June 15, 2024).
Berenguer, C.V., García-Cansino, L., García, M.�., Marina, M.L., Câmara, J.S., & Pereira, J.A.M. (2023, June 19). Microextraction Approaches Used to Assess Food Safety. In Encyclopedia.
Berenguer, Cristina V., et al. "Microextraction Approaches Used to Assess Food Safety." Encyclopedia. Web. 19 June, 2023.
Microextraction Approaches Used to Assess Food Safety

The use of microextraction techniques to survey the presence of contaminants in the food chain is very advantageous, involving simpler and faster protocols, reduced amounts of solvents and samples, and consequently, reduced waste produced during analysis while conserving a high potential for automation. Additionally, this higher greener profile of the microextraction techniques will boost a progressive substitution of conventional extraction approaches by microextraction processes in most analytical applications, including the survey of food chain safety.

microextraction food safety fruit pesticides vegetables antibiotics

1. Introduction

Today’s consumers are increasingly concerned about agriculture, nutrition, and sustainability, and they want to know where food comes from, how it was grown, what kind of industrial processes it suffered, and if it contains natural/synthetic food additives or not [1]. While fresh fruits and vegetables are important sources of phytonutrients such as polyphenols, vitamins, minerals, and fibres, they may also contain contaminants such as pesticides, antibiotics, or food preservatives [2]. Farmers use these contaminants to protect their crops and promote growth. Without suitable pest control measures, farmers could lose up to 40% of their yield, requiring more land, water, seed, tractor fuel, labour hours, and pest-control products to continue their activities [3][4]. However, the passive consumption of these molecules can have serious consequences for human health.
To address these concerns, many countries have strict regulations concerning the Maximum Residue Limits (MRLs) for pesticides in food [5]. The European Union (EU), for example, has established MRLs for 315 pesticides, with a default limit of 0.01 mg kg−1 for new pesticides [5] and the European Food Safety Authority (EFSA) prepares annual reports on pesticide residues in foodstuffs to control these MRLs [6]. The most recent report, approved in 2021 for the year 2019, found that pesticides exceeding their MRLs were present in almost 4% of the samples analysed, highlighting the importance of controlling pesticide presence in food for human health [6]. Another major concern is the presence of antibiotics in fruits and vegetables, which can promote antibiotic resistance and compromise food safety and the consumer’s trust in the food chain [7][8][9]. Antibiotics can enter these samples using natural fertilizers derived from human or animal faeces processing.
The use of food preservatives can also impact human health [10]. Sulphites, for example, are marketed as preservatives and can be classified as antioxidants, antimicrobials, and antibrowning agents [11]. However, they can also have anti-nutritional consequences by promoting the degradation of vitamin B1 [10].
Different extraction techniques can be employed to assess food safety. This selection depends on several factors, with the nature of the target analytes as one of the most important. Regardless of the target analytes, most methods currently developed still rely on conventional techniques, requiring large sample volumes and organic solvents along with laborious, time-consuming, and complex protocols. However, the growing concerns with the environment and planet sustainability are boosting the interest in the development of microextraction approaches based on green analytical chemistry principles.
Most microextraction techniques employ the same preparation principles as conventional methods with enhanced analytical performance. Additionally, these approaches possess simple and faster extraction procedures, in which lower sample and solvent volumes are used [12].

2. Microextraction Approaches

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 [13]. 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 [13][14]. 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][13].
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 [13]. 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 Arthur and Pawliszyn in 1987 [15], 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][13]. 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 [13]. 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 Câmara 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 [14][16]. This technique requires low solvent volumes and shorter sample preparation times and can be applied to smaller samples (volume 10–250 μL) [12][13].
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 automated process in which it is possible to use the same syringe for sample extraction and extract injection in the analytical instrumentations [12][13]. However, when using higher sample volumes, this device often shows limitations.
The technique of dispersive solid-phase extraction (dSPE) and its related formats involve combining the sample matrix with the sorbent to effectively capture the desired analytes in the sorbent particles. This can be accomplished by either column packing or using SPE tubes with vacuum or centrifugation. The analytes are then extracted using an appropriate elution solvent. Additionally, magnetic nanoparticles can be utilized to enhance the extraction process, allowing for easy isolation of the sorbent particles and analyte retention through decantation using a simple magnet [13]. The dSPE is also widely used as a clean-up procedure in the two steps QuEChERS/dSPE methodology previously referred to.

2.2. Liquid-Based Microextraction Techniques

Conventional LLE techniques present a few limitations, including emulsion formation, long preparation time, and the use of high volumes of toxic organic solvents. Moreover, the evaporation of the solvent is inevitable, as well as sample reconstitution. To overcome these issues, miniaturized liquid-phase extraction (µLPE) techniques that use microliters of organic solvent to accomplish the selective isolation, preconcentration of the analytes, and clean-up of the sample were developed [12]. These innovations related to the extraction and pre-concentration of analytes have resulted in the development of emergent approaches such as liquid–liquid microextraction (LLME) and dispersive liquid–liquid microextraction (DLLME) [13][14].
DLLME and its modifications offer several advantages; namely, a high pre-concentration factor for the target analytes, small sample volumes, low consumption of solvents, a high extraction efficiency, a low cost, simplicity, and a high enrichment factor [12][13]. These techniques can also be combined with almost every analytical measurement technique [13]. In ionic liquid-based DLLME (IL-DLLME), ILs are used as an alternative to hazardous solvents due to their thermal stability, reusability, high reaction efficiency, and ability to dissolve both organic and inorganic compounds [13]. Due to the cation’s fine structure and the anion’s identity, it is possible to modify the ILs’ properties according to the analytical purpose. Nevertheless, their high cost and toxicity remain the main disadvantages [13]. In ultrasound-assisted DLLME (UA-DLLME), ultrasound is applied to disperse the extraction solvent in the sample, which avoids the reduction of the analyte’s partition coefficient between water and the extracting solvent [12]. Single-drop microextraction (SDME), in which the extraction solvent is limited to a single drop, is related to DLLME and allows a great preconcentration factor. The drop is controlled by a microsyringe that loads and withdraws the drop from the solution [13].

2.3. The Potential of Microextraction Approaches

In the last decades, the use of microextraction as an alternative to conventional extraction approaches became very popular. The main reasons for this evolution are mainly simpler and less cumbersome experimental protocols that are easier and faster to perform and more prone to automation. These features limit the user’s intervention and allow a better analytical performance of the following analytical steps.
Among the microextraction approaches SPME is certainly one of the most used, and dozens of applications involving the extraction of pesticides and other food preservatives have been reported in the literature. SPME allows a relatively fast and easy sample extraction procedure and can be used in different modes, such as headspace (HS) [17] or direct immersion (DI) [2][18][19]. Furthermore, many variations of the sorbent material and format are commercially available [20][21][22] and both volatile compounds analysed by GC, and non-volatile, such as diazinon and chlorpyrifos, analysed by LC [20], have been reported.


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