Recent advances in microwave-assisted extraction of trace organic pollutants from food and environmental samples

Recent advances in microwave-assisted extraction of trace organic pollutants from food and environmental samples

Accepted Manuscript Title: Recent advances in microwave-assisted extraction of trace organic pollutants from food and environmental samples Author: Hu...

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Accepted Manuscript Title: Recent advances in microwave-assisted extraction of trace organic pollutants from food and environmental samples Author: Hui Wang, Jie Ding, Nanqi Ren PII: DOI: Reference:

S0165-9936(15)00212-5 http://dx.doi.org/doi: 10.1016/j.trac.2015.05.005 TRAC 14501

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Trends in Analytical Chemistry

Please cite this article as: Hui Wang, Jie Ding, Nanqi Ren, Recent advances in microwaveassisted extraction of trace organic pollutants from food and environmental samples, Trends in Analytical Chemistry (2015), http://dx.doi.org/doi: 10.1016/j.trac.2015.05.005. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Recent advances in microwave-assisted extraction of trace organic pollutants from food and environmental samples Hui Wang, Jie Ding, Nanqi Ren * State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China

HIGHLIGHTS  An overview of microwave-assisted extraction (MAE) for trace organic analysis  Recent advances in MAE from the perspective of green analytical chemistry  MAE applied to food and environmental analysis in the period 2008–14  Comparison of advantages and disadvantages of MAE with other techniques

ABSTRACT In recent years, microwave-assisted extraction (MAE) has attracted growing interest, as it is an effective method for the rapid extraction of a number of trace organic pollutants from food and environmental samples, due to advantages in facilitating on-line measurements, high efficiency, significantly lower extraction time and solvent consumption than classical techniques. This review describes recent advances of MAE from the perspective of green analytical chemistry, and summarizes the main results in applications published in the period 2008–14. Finally, we compare the performance of this technique to that of traditional extraction and other recent techniques. Keywords: Analytical application Environmental matrix Extraction Food sample Gas chromatography-tandem mass spectrometry Green analytical chemistry High-performance liquid chromatography Microwave-assisted extraction Sample preparation Trace organic pollutant Abbreviations: ASE, Accelerated solvent extraction; DLLME, Dispersive liquid-liquid microextraction; DMAE, Dynamic microwave-assisted extraction; ECD, Electron-capture detector; FD, Fluorescence detection;

FID,

Flame-ionization detection; FMAE, Focused microwave-assisted extraction; GAC, Green analytical chemistry; GC, Gas chromatography; GC-MS/MS, Gas chromatography-tandem mass spectrometry; GPC, Gel-permeation chromatography; HAA, Heterocyclic aromatic amine; HPLC, High-performance liquid chromatography; LC-MS/MS, Liquid chromatography-tandem mass spectrometry; LOD, Limit of detection; LOQ, Limit of quantification; MAE, Microwave-assisted extraction; MAME, Microwave-assisted micellar extraction; MASE, Microwave assisted steam 1 Page 1 of 23

extraction; MASSE, Microwave-accelerated selective Soxhlet extraction; MS, Mass spectrometry; PAH, Polycyclic aromatic hydrocarbon; PBDE, Polybrominated diphenyl ether; PLE, Pressurized liquid extraction; PMAE, Pressurized microwave-assisted extraction; PM 2.5 and PM 10, Particulate matter; P&T, Purge-and-trap; SBME, Solvent-bar microextraction; SE, Soxhlet extraction; RSD, Relative standard deviations; SFOD, Solidification of floating organic drop; SPE, Solid-phase extraction; SPME, Solid-phase microextraction; tan δ, Dissipation factor; UAE, Ultrasound-assisted extraction; UAEME, Ultrasound-assisted emulsification microextraction; UHPLC, Ultra HPLC; UMAE, Ultrasonic microwave-assisted extraction; µ-ECD, Micro-electron capture detector; µ-SPE, Micro-solid phase extraction. Ionic liquids: C16C4Im-Br, 1-hexadecyl-3-butylimidazolium bromide; C16C4Im-NTf2, 1-hexadecyl-3-butylimidazolium bis[(trifluoromethane)sulfonyl] imide; HDMIm-Br, 1-hexadecyl-3-methylimidazolium bromide; LiNTf2, Lithium bis[(trifluoromethane)sulfonyl] imide; [N8881][Tf2N], Trioctylmethylammonium bis(trifluoromethylsulfonyl) imide; NaPF6, Sodium hexafluorophosphate * Corresponding author. Tel./Fax: +86 451-86286809. E-mail address: [email protected] (N. Ren)

1. Introduction Sample preparation plays an essential and crucial role in the whole analytical procedure, especially for analyzing solid samples. Most analytical instruments are unable to handle matrices directly and some forms of pretreatment are required to extract and to enrichment the analytes, particularly in food and environmental samples, which are characterized by complex matrices and the presence of trace and ultra-trace amounts of analytes. The most frequently mentioned problems arising in preparing samples for analysis are usually expense in terms of time and reagent consumption, loss of analytes and contamination. Ideally, sample preparation should be fast, accurate, precise, and environment friendly. The application of microwave energy for sample preparation was first proposed in 1975 [1]. Microwave energy is a non-ionizing radiation (frequency 300–300000 MHz), which can penetrate into certain materials and interact with the polar components to generate heat. Heating of microwave energy acts directly on molecules by ionic conduction and rotation of dipoles [2,3]. Ionic conduction refers to the electrophoretic migration of the charge carriers (e.g., ions and electrons) under the influence of the electric field produced by microwave [4]. Dipole rotation relates to alternate movement of polar molecules that try to line up with the electric field [5]. Multiple collisions from this agitation of molecules generate energy release, which results in rapid heating. The extraction of organic compounds by microwave irradiation appeared with the work of Ganzler et al. in 1986 [6]. Since then, the technique has attracted growing interest, and it has been extensively used in analytical chemistry. Numerous applications have been reported for assisting the extraction of organic compounds from food and environment [7–9]. One of the main advantages of using microwave-assisted extraction (MAE) is the reduction of extraction time, which can mainly be attributed to the difference in the heating performance of microwave and conventional heating [10]. Additionally, MAE allows on-line coupling to other analytical steps and the possibility of running multiple samples [11,12]. MAE is clearly greener than more classical methods and brings the following advantages from the perspective of green analytical chemistry (GAC) [13]: (1) significant shortening of the time for many processes with subsequent savings in energy; 2 Page 2 of 23

use of less solvents or safer solvents, which reduces waste generation and avoids pollution; achievement of low-cost methods with increased productivity; provides the possibility of on-line coupling to other analytical steps; and enables partial or total automation of the analytical process, reduces analysis time, decreases analyte loss, and increases personal safety. In recent years, several reviews [5,14] were published on the use of microwaves for solid-sample extraction. To avoid major overlap with previously published articles, we focus our attention on the applications of MAE to extract trace-organic pollutants from food and environmental matrices published since 2008, with special emphasis on describing different aspects of recent interesting applications of MAE. This review attempts to demonstrate the growing trend of MAE from the perspective of GAC, based on two factors: (a) efficient MAE equipment; and, (b) environment-friendly extraction mediums. Finally, the performance of MAE is compared to that of other techniques, classical or recent. (2) (3) (4) (5)

2. Efficient microwave-assisted extraction equipment Generally, MAE devices comprise a closed extraction vessel under controlled pressure and temperature or a focused microwave oven at atmospheric pressure. These two technologies are commonly named pressurized MAE (PMAE) or focused MAE (FMAE), respectively. The PMAE system consists of a magnetron tube, an oven where the extraction vessels are set upon a turntable and monitoring devices for controlling temperature and pressure. In PMAE, the extractions are performed in some sealed extraction cells with microwave radiation, in static and batch mode. The increase in temperature and pressure accelerates extraction due to the ability of extraction solvent to absorb microwave energy. The closed system offers fast, efficient extraction with less solvent consumption, but it is susceptible to losses of volatile compounds and generally expensive due to its resistance to high pressure and its air-tightness [15]. FMAE involves an open MAE system developed to counter the shortcomings of the closed system, such as safety issues. The extractor design is based on the principles of a conventional Soxhlet extractor modified to facilitate accommodation of the sample-cartridge compartment in the irradiation zone of a microwave oven. Solvent distillation in the FMAE extractor could be achieved by electrical heating, which is independent of extractant polarity [16]. It is considered more suitable for extracting thermolabile compounds due to only part of the extraction cell being directly exposed to microwave radiation. The advantages and the disadvantages of FMAE were highlighted by Luque de Castro et al. [17]. Since the upper part of the extraction cell is connected to a reflux unit to condense vaporized solvent, sample throughput was limited. There is therefore a requirement to develop more efficient MAE methods, which overcome at least some limitations of the known processes. We discuss these modifications hereafter. 2.1. On-line MAE On-line MAE is carried out in a similar way to PMAE using a microwave oven equipped with a vessel. The sample is immersed in the extraction solvent and irradiated by microwaves. After the complete extraction, an aliquot of the extract is aspirated by a pump for further treatment. Sometimes, subsequent treatment is also completed in the extraction vessel. 3 Page 3 of 23

Fig. 1 shows an example of an on-line MAE system of the continuous flow configuration [18]. The extraction system comprised a household microwave oven equipped with a magnetron. The flow system consists of a high-pressure quaternary gradient pump for solvent delivery. The extract is carried by an aqueous stream and passed through a continuous filtration PTFE membrane, where the analytes are retained while the potential coextracted compounds go to waste. The analytes are eluted by means of an acetone stream and determined with an evaporative light-scattering detection system. Deng et al. designed an on-line microwave and purge-and-trap (P&T) device coupled with gas chromatography-mass spectrometry (GC-MS) for the determination of odors in sediment and fish tissues [19]. An inlet gas-transfer line was fixed at the dry purge valve of the P&T system, an outlet gas-transfer line was fixed to the cross of the P&T system and heated to prevent condensation of the target compounds, and the GC-MS was connected to the six-port valve of the P&T system. After extraction, the analytes were desorbed, then the system started to bake for cleaning, and the sample could be reloaded at this point. Compared with the off-line method, on-line MAE performed in a closed system could reduce sample contamination, analyte loss, and the chance of people being exposed to organic solvents. 2.2. Dynamic MAE (DMAE) A feature of DMAE is that analytes can transfer out of the extraction vessel as soon as they are extracted. This is especially important to avoid degradation of thermolabile analytes. Moreover, the extract can be filtered on-line, and DMAE can couple with other sample pretreatment and analytical steps. DMAE is usually performed in one of two systems, namely mono-sample DMAE and multi-sample DMAE. In mono-sample DMAE, an extraction solvent is introduced with a high-pressure pump or peristaltic pump [11]. The solvent is pumped through the sample, and then extracted analyte is directly transferred to the next step, such as clean-up with solid-phase extraction (SPE) or detection by high-performance liquid chromatography (HPLC) [20] and spectrophotometry [21]. In the study by Chen et al. [21], a AWGY-20 microwave source was applied to provide microwave energy, a TM010 microwave-resonance cavity was applied as the microwave coupling device, and two tuning screws in the cavity were used to tune the reflected power (Fig. 2A). The analytes were extracted under the action of microwave energy, and then directly introduced into the SPE column for preconcentration of analytes and clean-up of the sample matrix. The extraction and clean-up procedures were performed simultaneously in a single step, so the overall pretreatment time was reduced. However, sample throughput and amounts were limited. Moreover, as the pressure of the system was raised, that could cause extract leakage at the joints of tubes [14]. To overcome the drawbacks of mono-sample DMAE, a multi-sample DMAE device was assembled in 2011. It consisted of a solvent-storage container, a household microwave oven, a vacuum SPE manifold and a vacuum pump (Fig. 2B). The vacuum pump was utilized to deliver solvent. The extraction-solvent flow rate could be adjusted by a vacuum valve and flow-rate control valves [12]. The extraction and clean-up of 20 samples could be completed simultaneously in a short period. Compared with mono-sample DMAE method, multi-sample DMAE improved the sample throughput and microwave-energy utilization. Moreover, the solvent was pumped into extraction vessels under the negative pressure created by the vacuum pump. It is important to avoid leakage of solvent into the microwave cavity, so the safety of the microwave system was improved. 4 Page 4 of 23

2.3. Ultrasonic MAE (UMAE) Enhancement of the mass-transfer mechanism in extraction can be achieved by UMAE. Ultrasonic energy allows greater penetration of solvent into the sample matrix, increases the contact surface area, and generates expansions or compressions, thus enhancing the extraction efficiency. MAE heats the extract quickly and accelerates the extraction process for adsorption and desorption of the targeted compounds from the matrix, but its disadvantage is inhomogeneous heating [22]. Hence, coupling microwave extraction with ultrasound extraction is a complementary technique and presents some more advantages. Ultrasonication can be implemented in MAE systems in two ways:  directly to the sample by an ultrasonic probe; or,  indirectly through the walls of the sample container using a water bath. The ultrasonic bath transmits high energy and high-frequency sound waves into a fluid-filled container, which works with multi-frequency units operated simultaneously ultrasonic transducers with different frequency. Ultrasonic probe focus their energy on a localized sample zone, thereby providing more efficient cavitation in the liquid than the bath. However, literature indicated that most researchers use ultrasonic baths, although the extraction time (15–120 min) is much longer than with the ultrasonic probe (2–3 min).

3. Environment-friendly extraction mediums The extraction medium is obviously important in MAE. It should efficiently solubilize the analytes of interest and have excellent microwave-absorbing properties. The dissipation factor (tan δ) is a measure of the ability of the solvent to absorb microwave energy and dissipate that energy in the form of heat [2]. The dissipation factor is expressed as the quotient: tan δ = e"/e' where e" is the dielectric loss factor, indicative of the efficiency of converting electromagnetic radiation to heat, and e' is the dielectric constant describing the ability of molecules to be polarized by the electric field. Polar organic solvents have high tan δ values and are preferable for microwave-promoted reactions [23]. One of the main principles of green sample preparation is to develop an extraction medium alternative to toxic organic solvents, and is the basis for the progress of various cleaner chemical technologies. There has been a great deal of interest in developing procedures based on environment-friendly solvents in MAE. 3.1. Microwave-assisted micellar extraction (MAME) In recent years, MAME, which uses a micellar (surfactant-rich) system to substitute organic solvent as extractant in MAE, has been applied to the extraction of different compounds from solid samples. In order to enhance both extraction speed and efficiency, microwave energy is used while maintaining the sample at a suitable temperature. At this point, micelles of surfactant are formed, with analytes isolated and enriched in them. Fig. 3 shows the three key steps for the operations of MAME: (1) addition of surfactant to the sample; 5 Page 5 of 23

(2) microwave-assisted micellar extraction for some time; and, (3) suitable treatment of the extract. Before injecting the extract into the analytical instrument, the MAME extract obtained should be suitably prepared (Step III, Fig. 3). Separation of two phases requires appropriate experimental conditions depending on the nature of the surfactant. Sometimes, analytes in the MAME extract were concentrated with the help of centrifugation after equilibrium at high temperature and adding salt reagent (Step III a, Fig. 3) [24]. The analytes in the micelle-rich phase could be directly injected into HPLC for subsequent separation and detection. As the micelle-rich phase is viscous and cannot be injected directly into some analysis apparatus (e.g., LC-MS/MS), then additional clean-up and concentration of the MAME extract should be employed, such as SPE [25] or solid-phase micro-extraction (SPME) [26] (Step III b and c, Fig. 3). For SPE, MAME extracts went through the SPE cartridge, and the retained analytes were eluted and analyzed. For SPME, SPME fibers were directly immersed into the MAME extract under optimized conditions, and thereafter the analytes were desorbed from the fiber by a suitable solvent. 3.2. Ionic liquid-based MAE Ionic liquids (ILs) are liquid salts with melting points close to or below room temperature, and are generally considered to be more environmentally friendly than conventional organic solvents. The physicochemical properties of ILs depend on the nature and size of both their cation and anion constituents [27]. ILs can act as surfactants, their application in analytical chemistry is merited because ILs have some unique properties, such as negligible vapor pressure, good thermal stability, tunable viscosity and miscibility with water and organic solvents [28]. ILs absorb microwave radiation extremely well and transfer energy quickly by ionic conduction. This strategy may improve extraction efficiency and speed up analysis. There are several publications regarding ILs used in application of MAE for organic-compound determination. 3.3. Microwave-assisted aqueous-solution extraction Recently, aqueous solutions or steam were used as green solvents to extract organic pollutants from solid samples. Sturini et al. developed the “organic solvent-free” MAE method to isolate fluoroquinolones (FQs) from soil using an aqueous solution of 20% (w/v) Mg(NO3)2 as extract agent [29], since deprotonated carboxylic acid groups of FQs are able to form stable chelates with several divalent and trivalent metal ions [e.g., Ca (II), Mg (II) and Al (III)] [30]. Selected acidic pharmaceuticals (e.g., ibuprofen, naproxen, ketoprofen, and diclofenac) in sewage sludge were analyzed based on MAE using water as extractant to reduce the matrix effect compared with organic solvents. However, the disadvantage of applying water as extractant was that fats and oils together with detergents in sewage sludge resulted in a hard, disrupting, colloidal solution [31]. Song et al. presented an on-line MAE method to extract carbamate pesticides in rice with water steam [32]. The extract obtained was immediately applied on a C18 SPE cartridge for clean-up and concentration. The eluate containing target compounds was finally analyzed by LC-MS/MS. The limits of detection (LODs) were 1.1–4.2 ng g-1. In recent years, enzymatic digestion was widely accepted as a sample-preparation method for the analysis of pharmaceuticals in biological matrices, to resolve the problem of the analyte being bound to proteins and peptides. Fernandez-Torres et al. developed an enzymatic-MAE method for 6 Page 6 of 23

the simultaneous determination of 11 veterinary antibiotics in food of marine origin [33]. A mixture of 5 mL deionized water and 50 µL Proteinase-K solutions was used as extractant. To avoid inhibition of enzyme activity, 50-W irradiation power and 5-min irradiation time were selected. In general, worse recoveries of antibiotics were obtained and at longer times and greater irradiation powers, and undesirable substances and degradation of analytes followed.

4. Main applications The use of MAE for extracting pollutants from complex samples attracted considerable interest in the past few years. This review covers applications of the technique for isolating trace organic pollutants from food (Table 1) and environmental (Table 2) matrices published since 2008. However, exploitation of MAE in isolating bioactive compounds and secondary metabolites produced from food and plants is outside the scope of this review. In food and environmental analysis using MAE, trace pesticides (e.g., avermectin, pyrethroid, triazines and organochlorine), aromatic fused-ring compounds (e.g., polybrominated diphenyl ethers, polycyclic aromatic hydrocarbons and heterocyclic aromatic amines), and trace pharmaceuticals and hormones (e.g., sulfonamides, FQs and estrogens) constitute the three main categories for analysis. 4.1. Pesticides Several kinds of pesticides, insecticides, fungicides and herbicides are used to prevent weed growth and protect crops against pest damage [34,35]. Due to bad agricultural practices while applying these chemicals, residues of several pesticides can be found in food and the environment, not only affecting the quality of food but also threatening human health [36]. The analyses of trace pesticides by MAE in tomato [37], cereals [32,38,39], ginseng [40], almond milk [41], mussel tissue [42], fish [43], soil [44–47], particulate matter [48], seaweed [49], and sediment [50,51] have been described. After homogenization, samples were extracted with a water-miscible solvent under the microwave irradiation. The extract was cleaned up by SPE or SPME, and pesticides were analyzed by HPLC or GC-MS. Merdassa et al. developed a one-step MAE procedure to extract simultaneously organophosphorus pesticide and fungicide residues in soil [44,46]. The analytes in extracts were analyzed directly by GC-MS or HPLC without any further clean-up, and parameters affecting the MAE process (e.g., type and volume of extraction solvent, irradiation power and salt addition) were optimized. Su et al. coupled solventless MAE with ultrasound-assisted emulsification microextraction (UAEME) for the determination of organophosphorus pesticides in soils [47]. A homemade glass tube inbuilt with a scaled capillary tube was used as an extraction device to collect and to measure the separated extractant phase easily. Compared to other methods, the method was shown to be highly competitive in terms of sensitivity, cost, and analysis speed. A method for analysis of avermectins in soils was developed by MAE-SPE [45]. In order to shorten the chromatographic run, separation was performed in ultra-HPLC (UHPLC) conditions, and analyzed by UHPLC-MS/MS. The results prove that MAE efficiency of avermectins depended on the properties of the soil. A similar approach for multi-residue analysis of 16 organochlorine insecticides in mussel tissue 7 Page 7 of 23

was proposed [42]. The method is superior in terms of sample throughput and environmental friendliness of the extraction solvent, and simpler in the clean-up procedure, and offers the confirmation capabilities of the mass detector for an extended pesticide list. Zhang et al. showed that the concentration of organochlorine pesticides extracted from fish muscle tissue by MAE significantly decreased after the samples were freeze-dried [43], apparently because of the resistance of organochlorine pesticides associated with freeze-dried muscle protein to solvent extraction. The extractability can be recovered by adding water prior to extraction. Li et al. developed the UMAE-SPE method to isolate organophosphate and pyrethroid insecticides from sediment [51]. They stressed the importance of solvent types. For polar pesticides, a solvent with a higher polarity (such as acetone) was recommended to provide the required recoveries. Due to a significant reduction in extraction time, the UAME method greatly improved extraction efficiency of thermally-labile and volatile insecticides. Guillet et al. developed the FMAE-SPME method to determine 25 pesticides used in tomato cultivation [37]. Using microwaves, the sample temperature increased not to exceed 65°C, in order to minimize the possible degradation of thermolabile pesticides. SPME fibers were immersed into the extract for 30–45 min, and were then directly introduced into the chromatographic injector port for desorption. A similar application of MAE-SPME was presented by Carvalho et al.[50]. Complete automation of the SPME procedure increased the sample throughput, including standard addition for calibration purposes. We presented a rapid analytical method based on DMAE combined with solidification of floating organic drop (SFOD) for determination of triazine residues in cereal samples [38]. The approach combined the advantages of DMAE and SFOD, and up to 15 samples could be treated simultaneously in 16 min. The triazines were extracted with 1 mL of methanol containing 90 µL of 1-dodecanol and following with 10 mL of water under the action of microwave energy. After salting out, centrifugation and cooling, the 1-dodecanol drop that contained the target analytes was solidified and transferred for analysis by HPLC-UV. The method was successfully applied to the analysis of 10 cereals and the recoveries of the triazines for the spiked samples were in the range 80–102%. Wu et al. applied medium-assisted non-polar solvent DMAE to extract organophosphorus pesticides from cereal samples [39]. Without adding any polar solvent, graphite powders were used as a microwave absorption medium to transform microwave energy into heat energy. Hexane could extract 10 organophosphorus pesticides completely within 200 s, and the extract was directly analyzed by GC-MS without any clean-up process. Microwave-accelerated selective Soxhlet extraction (MASSE) was evaluated for determination of organophosphorus and carbamate pesticides in ginseng by Zhou et al. [40]. During the extraction procedure, both target analytes and interfering components were extracted from the sample into the extraction solvent enhanced by microwave irradiation. After the solvent flowed through the sorbent, the interfering components were adsorbed by the sorbent, and the target analytes remaining in the solvent were collected in the extraction bottle. The sorbent used in this technique proved to have a nice clean-up ability, which resulted from the interactions of the polar functional groups. In optimized conditions, recoveries in the range 72.0–110.1% were achieved with relative standard deviations (RSDs) less than 7.1%. Coscollà et al. presented a method to determine 40 pesticides in airborne particulate matter (PM 10) at trace level using GC-MS/MS [48]. The procedure included extraction of PM 10-bound pesticides by MAE followed by gel-permeation chromatography (GPC) clean-up. The author stressed that the benefit of the GPC clean-up was decreased matrix effect. The method was applied 8 Page 8 of 23

to 38 samples, and 18 of 40 pesticides investigated were found in at least one sample, with concentrations of 1.32–625.80 pg m−3. Besides organic solvents being used as extracting solvents, some emerging solvents were applied in MAE. Wang et al. [41] developed a MAE method using ILs for separating pyrethroid pesticides from various aqueous media, such as almond milk, honey, water and fruits. Six different ILs were preliminarily tested as extraction solvents, and optimal results were achieved using methanol as a dispersal solvent with trioctylmethylammonium bis(trifluoromethylsulfonyl)imide ([N8881][Tf2N]) as the extraction solvent at a microwave power of 200 W for 60 s. Organochlorine pesticides in seaweeds were extracted with MAME using a non-ionic surfactant (Polyoxyethylene 10 Lauryl Ether) by Moreno et al. [49]. SPME and SPE were used to clean-up and concentrate MAME extract prior the analysis by HPLC. Average pesticide recoveries in the range 80.5–104.3% for MAME-SPME and 73.9–111.5% for MAME-SPE were obtained. RSDs were lower than 10.3% and 5.3%, respectively, for all recoveries tested. 4.2. Aromatic fused-ring compounds Polybrominated diphenyl ethers (PBDEs) belong to the group of brominated flame retardants and are widely used as additives to a great variety of consumer products to prevent or to retard the spread of fire [52]. Polycyclic aromatic hydrocarbons (PAHs) comprise the largest group of chemical compounds known to be cancer-causing agents, and may be formed and released during the incomplete combustion or thermal decomposition of organic material [53]. Heterocyclic aromatic amines (HAAs) are compounds with high carcinogenic potential, formed during the cooking process at high temperatures of protein-rich foods [54]. Recently, several reports described the analysis of PBDEs, PAHs and HAAs in particulate matter [55], soil [56–58], sediment [59,60], beefburger [54], fish [7,61], tea [62] and toasted cereals [63,64]. Both PMAE and FMAE were used. A sensitive, selective method for the determination of 12 PBDEs in airborne particulate matter (PM 2.5) at trace level was developed [55]. It included extraction PM 2.5-bound PBDEs by PMAE followed by GPC clean-up and determination by GC-MS/MS using a programmed temperature vaporizer in large-volume-injection mode to introduce the sample to the chromatographic system. A single-step extraction-clean-up procedure involving PMAE and microSPE (µ-SPE) was developed for the analysis of PAHs from soil samples [56]. µ-SPE is a new extraction procedure that makes use of a sorbent enclosed within a sealed polypropylene membrane envelope. Soil sample, the µ-SPE device and 10 mL of water were added to the PMAE vessel. After extraction, the µ-SPE device was removed, and the analyte were eluted from the device using acetonitrile with sonication. Subsequently, Guo et al. combined PMAE with solvent-bar microextraction (SBME) to analyze PAHs in environmental soil samples by GC-MS [58]. An interesting feature of this procedure is that SBME was conducted simultaneously with MAE, and the extract from the SBME could be directly analyzed by GC-MS without any separate clean-up or preconcentration process. It is also remarkable that the procedure was environmentally benign, since water was used as the extraction solvent in MAE, and only several µL of organic solvent were used in SBME. Lv et al. evaluated 16 PAHs in soil by PMAE-SPE-GC-MS [57]. The total concentrations of tested PAHs in four districts of Tianjin city (China) were 58.5–2748.3 ng g-1, 36.1–6734.7 ng g-1, 58.5–4502.5 ng g-1 and 29.7–852.5 ng g-1 and the averages of total concentration of PAHs were 600.5 ng g-1, 933.6 ng g-1, 640.8 ng g-1 257.3 ng g-1, respectively. The combination of a matrix-isopotential synchronous fluorescence technique with a 9 Page 9 of 23

variable-angle synchronous fluorescence technique was a novel approach to rapid, selective determination of PAHs in tea samples free from tedious clean-up procedures [62]. The LODs for benzo(a)pyrene, benzo(k)fluoranthene, and anthracene in tea were 0.1–-0.28 μg kg-1, 0.55–0.89 μg kg-1 and 0.64-3.58 μg kg-1, respectively, depending on various teas, with satisfactory recoveries of 77.1–116%. Ramalhosa et al. [7] presented a method for the determination of 18 PAHs in fish samples that was validated by MAE-HPLC-fluorescence detection (FD). Response-surface methodology was used to find the optimal extraction parameters, and 20 min of extraction, 110°C, 10 mL of acetonitrile and medium stirring speed were the optimal conditions selected. Dispersive liquid-liquid microextraction (DLLME) was used as clean-up step coupled with MAE-GC-MS for extraction and quantification of 16 PAHs in smoked fish [61]. Fish samples were extracted with KOH-ethanol in the PMAE system. For DLLME, 500 µL of acetone (disperser solvent) containing 100 µL of ethylene tetrachloride (extraction solvent) were rapidly injected by syringe into the extract solution, forming a cloudy solution. Phase separation was performed by centrifugation, and the precipitated phase was analyzed by GC-MS in selected-ion-monitoring mode. The method provided excellent enrichment factors (in the range 244–373 for 16 PAHs) and good repeatability (with RSDs of 2.8–9%) for spiked smoked fish. There have been a few MAE analytical methods using ILs for determination of PAHs in complex matrices [59,63,64]. Germán-Hernández et al. used IL aggregate 1-hexadecyl-3-butylimidazolium bromide (C16C4Im-Br) as the extraction agent for the determination of 15+1 EU PAHs contained in toasted cereals by HPLC-FD [63]. Under optimized conditions, extraction recoveries were 70.1–109% and precision values were lower than 12.6%. The authors emphasized that the method required a small amount of IL to generate an adequate extractant solution (77 mg), and was greener than conventional extraction methods requiring high volumes of organic solvents. In 2012, they modified this method, and developed an in situ preconcentration method [64]. C16C4Im-Br extract originating from the MAE of toasted cereals was mixed with lithium bis[(trifluoromethane)sulfonyl] imide (LiNTf2). A turbid solution then appeared, and after vortexing, centrifugation, freezing, a microdroplet (C16C4Im-NTf2 containing PAHs) was formed at the bottom of the tube. The diluted microdroplet was then injected into HPLC without any additional clean-up step. The extraction efficiency of the method was satisfactory, with average efficiencies of 80–95%, and precision values lower than 14%. A method to extract PAHs from sediments was carried out using aqueous solutions containing aggregates of IL 1-hexadecyl-3-methylimidazolium bromide (HDMIm-Br) as the extracting medium [59]. PMAE was used to accelerate the extraction, followed by HPLC-FD without clean-up steps to remove the IL prior to injection. The optimized method gave average absolute recoveries of 91.1% for six of the seven PAHs studied, with RSDs lower than 10.4%. According to the authors, the extraction of marine sediments with micellar media is generally more difficult to accomplish when using fine fractions of the sediments. MAE combined with DLLME using an IL generated in situ proved to be an efficient, fast, reproducible and sensitive methodology to analyze non-polar HAAs in cooked beefburgers by Mesa et al. [54]. The MAE procedure consisted of a clean-up step with n-heptane and a subsequent dissolution step in basic media to desorb the analytes from the matrix. Next, an aqueous solution of IL 1-octyl-3-methylimidazolium tetrafluoroborate, [OMIm][BF4] was mixed with an aqueous solution of sodium hexafluorophosphate (NaPF6) within the sample solution. Thus, the water-insoluble 1-octyl-3-methylimidazolium hexafluorophosphate, [OMIm][PF6], was formed in situ. After fluidification of the IL phase, [OMIm][PF6] containing HAAs were analyzed by 10 Page 10 of 23

HPLC-FD. Considering the complexity of the matrix sample, the extraction methodology was reproducible and fast, since cleaning sample and desorption of analytes from the solid matrix were done simultaneously in the microwave oven. 4.3. Pharmaceuticals and hormones Human and veterinary drugs are continually being released into the environment mainly as a result of manufacturing processes, improper disposal or metabolic excretion [65]. Pharmaceutical compounds are broadly employed in food-animal agriculture worldwide for prophylactic or therapeutic purposes, including antimicrobials, antibiotics and anti-inflammatory drugs. Hormones are defined by their chemical structure and their effect on the estrous cycle. They act as endocrine-disrupting chemicals that interfere with the endocrine system, and disrupt the physiological functions of hormones [66]. Estrogens may originate from natural processes and industrial activities. MAE has been used for the trace analysis of pharmaceuticals and hormones in chicken [67], fish [68], soil [69, 70], sediment [25,71,72] and sludge [73,74]. We presented a multi-sample DMAE method to analyze sulfonamides [67] and steroid hormones [68] in chicken and fish, respectively. It was an effective technique for reducing the sample-preparation time and solvent consumption. The total pretreatment time for 15–20 samples was less than 20 min. A method based on mono-sample DMAE coupled with SPE and LC-MS/MS was developed for the determination of sulfonamides in soil [69]. The DMAE parameters were optimized by the Box-Behnken design. Maximum extraction efficiency was achieved using 320 W of microwave power; 12 mL of extraction solvent; and, 0.8 mL min−1 of extraction solvent flow rate. The mean values of RSDs of intra-day and inter-day were 2.7–5.3% and 5.6–6.7%, respectively. There is limited study devoted to the analysis of estrogens from solid samples because of the complexity of sample processing and the requirement for low LODs. Recently, MAE coupled with LC-MS/MS detection for estrogens in sediments and sewage sludge was developed by Matějíček [71] and Vega-Morales et al. [73]. The MAE-LC-MS/MS method was optimized and provided increased selectivity and sensitivity with lower LODs (90–250 pg g−1), and significant reductions in total analysis time and sample manipulation are the main advantages of the proposed method [71]. The extraction efficiency of MAE-SPE was similar for all compounds, when compared with the results from conventional extraction methodologies, but the advantages of MAE included low solvent consumption and short extraction time [73]. The method developed was then applied to analyze estradiol-mimicking-compounds in sewage-sludge samples from three wastewater treatment plants in Spain. All the analytes in the study, including nonylphenol, octylphenol, 17β-estradiol, estriol, 17α-ethynylestradiol and bisphenol-A were found in almost all samples in concentrations of 0.9–710.2 ng g−1. Azzouz and Ballesteros [70] described an improved method based on MAE coupled on-line with SPE for extraction and analysis of pharmaceuticals and hormones in soils, sediments and sludge using GC-MS/MS. The analytes, trapped on Oasis-HLB sorbent, were eluted with ethyl acetate, and derivatized using N,O-bis (trimethylsilyl) trifluoroacetamide and trimethylchlorosilane, and silylated derivatives were determined by GC-MS in the SIM mode. The optimized GC-MS/MS method allowed high selectivity and sensitivity, with LODs of 0.8–5.1 ng kg−1. A method for determining benzophenone-derived compounds in sediments was proposed using MAE-SPE followed by derivatization and analysis by GC-MS [72]. Sediment analysis revealed 11 Page 11 of 23

benzophenone to be present in concentrations up to 650 ng g−1, whereas concentrations of other compounds were considerably lower (32 ng L−1). Cueva-Mestanza et al. [25] developed a cost-effective MAME-SPE method for the simultaneous determination of eight pharmaceutical compounds in sediment samples. A non-ionic surfactant (polyoxyethylene 10 lauryl ether) was used as extractant. Relative recoveries for spiked sediment samples were over 70% and RSDs were under 11% for all recoveries tested. LODs were 4–167 ng g−1. The use of cationic surfactant (hexadecyltrimethylammonium bromide) as extractant was successfully employed with MAME and LC-MS/MS for the determination of FQ antibiotics in coastal marine sediments and sewage-sludge samples [74]. In addition to providing the sensitivity needed for the determination of FQs in real samples, this method is an environment-friendly process because a biodegradable extractant is used. Under optimal conditions, recoveries were obtained greater than 73% with RSDs below 8%. The optimized method was applied in the determination of antibiotics in real solid samples. Four FQs (levofloxacin, norfloxacin, ciprofloxacin and enrofloxacin) were found and concentrations were 0.81–34.3 ng g−1 in the sediments and 3.43–206.1 ng g−1 in the sludge.

5. Comparison with other techniques Numerous studies reported the comparison of MAE with other extraction techniques, either classical or recent. We list and discuss the most common, easiest comparison results, in which the most remarkable characteristics of the MAE were reported by the authors and other methods were found in the literature for the same or similar target analytes. It is clearly seen (Table 3) that the choice of the optimum extraction technique is not easy. Pressurized liquid extraction (PLE) is fast due to the high degree of automation, but it requires a skilled operator to obtain reproducible data [75]. In contrast, Soxhlet extraction (SE) is applicable to a wide range of analytes from solid matrices, while the technique is slow (up to 24 h). The cost of the SE devices is relatively low in terms of capital expenditure, but high in terms of solvent consumption and disposal. Using this criterion would also eliminate accelerated solvent extraction (ASE) [76]. Of the remaining instrumental extraction techniques, PMAE and ultrasound-assisted extraction (UAE) offer different advantages and disadvantages. While PMAE is capable of extracting multiple samples simultaneously in a short time and provides the highest recoveries in comparison with UAE and PLE, the highest signal suppression was observed in PMAE extracts due to experimental conditions facilitating the extraction of matrix components [77]. UAE offered a simpler extraction procedure, requiring similar amounts of solvent to PMAE and PLE, but it requires longer analysis times. At the late stage of UAE, extraction for the solvent reached equilibrium, so it was hard to extract the analytes completely [77–79].

6. Conclusions and future developments This review provides a detailed description of the use of microwave energy to enhance the extraction of organic pollutants from food and environmental samples. All the reported applications show that MAE is a viable alternative to conventional techniques for complex matrices. Comparable efficiencies have been reported along with acceptable reproducibilities. Moreover, MAE offers a significant reduction in time and solvent consumption, and the opportunity to perform 12 Page 12 of 23

on-line coupling to other analytical steps. Evidence shows that MAE may compete favorably with recent techniques (such as UAE, PLE and ASE). Fortunately, there is still scope for improvement in terms of MAE performance and widening the fields of application. In this regard, development of MAE techniques for on-line monitoring will be essential. And environment-friendly extraction mediums used as extraction solvents will bring new simple, green and effective analytical methods in the near future. Acknowledgements The authors would like to thank the Development Program of China (863 Program) (Grant No.2011AA060905), the Program for New Century Excellent Talents in University (Grant No. NCET-11-0795), the National Water Pollution Control and Management Technology Major Projects (2013ZX07201007), the China Postdoctoral Science Foundation (No. 2014M561362) and the State Key Laboratory of Urban Water Resource and Environment (Harbin Institute of Technology) (No. 2015TS08) for their support of this study. References [1] A. Abu-Samra, J.S. Morris, S.R. Koirtyohann, Wet ashing of some biological samples in a microwave oven, Anal. Chem. 47 (1975) 1475-1477. [2] V. Camel, Microwave-assisted solvent extraction of environmental samples, Trends Anal. Chem. 19 (2000) 229-248. [3] C.S. Eskilsson, E. Björklund, Analytical-scale microwave-assisted extraction, J. Chromatogr. A 902 (2000) 227-250. [4] M.N. Nadagouda, T.F. Speth, R.S. Varma, Microwave-assisted green synthesis of silver nanostructures, Acc. Chem. Res. 44 (2011) 469-478. [5] L. Sanchez-Prado, C. Garcia-Jares, M. Llompart, Microwave-assisted extraction: Application to the determination of emerging pollutants in solid samples, J. Chromatogr. A 1217 (2010) 2390-2414. [6] K. Ganzler, A. Salgó, K. Valkó, Microwave extraction : A novel sample preparation method for chromatography, J. Chromatogr. A 371 (1986) 299-306. [7] M.J. Ramalhosa, P. Paíga, S. Morais, A.M.M. Sousa, M.P. Gonçalves, C. Delerue-Matos, M.B.P.P. Oliveira, Analysis of polycyclic aromatic hydrocarbons in fish: Optimisation and validation of microwave-assisted extraction, Food Chem. 135 (2012) 234-242. [8] H. Fujita, K. Honda, N. Hamada, G. Yasunaga, Y. Fujise, Validation of high-throughput measurement system with microwave-assisted extraction, fully automated sample preparation device, and gas chromatography-electron capture detector for determination of polychlorinated biphenyls in whale blubber, Chemosphere 74 (2009) 1069-1078. [9] S. Moret, G. Purcaro, L.S. Conte, Polycyclic aromatic hydrocarbons (PAHs) levels in propolis and propolis-based dietary supplements from the Italian market, Food Chem. 122 (2010) 333338. [10] E. Alonso-Rodríguez, J. Moreda-Piñeiro, P. López-Mahía, S. Muniategui-Lorenzo, E. Fernández-Fernández, D. Prada-Rodríguez, A. Moreda-Piñeiro, A. Bermejo-Barrera, P. Bermejo-Barrera, Pressurized liquid extraction of organometals and its feasibility for total metal extraction, Trends Anal. Chem. 25 ( 2006) 511-519.

13 Page 13 of 23

[11] H. Wang, L. Chen, Y. Xu, Q. Zeng, X. Zhang, Q. Zhao, L. Ding, Dynamic microwave-assisted extraction coupled on-line with clean-up for determination of caffeine in tea, LWT-Food Sci. Technol. 44 (2011) 1490-1495. [12] H. Wang, Q. Zhao, W. Song, Y. Xu, X. Zhang, Q. Zeng, H. Chen, L. Ding, N. Ren, High-throughput dynamic microwave-assisted extraction on-line coupled with solid-phase extraction for analysis of nicotine in mushroom, Talanta 85 (2011) 743-748. [13] L.H. Keith, L.U. Gron, J.L. Young, Green analytical methodologies, Chem. Rev. 107 ( 2007) 2695-2708. [14] L. Chen, D. Song, Y. Tian, L. Ding, A. Yu, H. Zhang, Application of on-line microwave sample-preparation techniques, Trends Anal. Chem. 27 (2008) 151-159. [15] H.-F. Zhang, X.-H. Yang, Y. Wang, Microwave assisted extraction of secondary metabolites from plants: Current status and future directions, Trends Food Sci. Tech. 22 (2011) 672-688. [16] J.L. Luque-García, M.D.L.d. Castro, Focused microwave-assisted Soxhlet extraction: devices and applications, Talanta 64 (2004) 571-577. [17] J.L. Luque-García, M.D.L.d. Castro, Where is microwave-based analytical equipment for solid sample pre-treatment going, Trends Anal. Chem. 22 (2003) 90-98. [18] E. Aguilera-Herrador, R. Lucena, S. Cárdenas, M. Valcárcel, Continuous flow configuration for total hydrocarbons index determination in soils by evaporative light scattering detection, J. Chromatogr. A 1141 (2007) 302-307. [19] X. Deng, P. Xie, M. Qi, G. Liang, J. Chen, Z. Ma, Y. Jiang, Microwave-assisted purge-and-trap extraction device coupled with gas chromatography and mass spectrometry for the determination of five predominant odors in sediment, fish tissues, and algal cells, J. Chromatogr. A 1219 (2012) 75–82. [20] L. Chen, H. Jin, L. Ding, H. Zhang, X. Wang, Z. Wang, J. Li, C. Qu, Y. Wang, H. Zhang, On-line coupling of dynamic microwave-assisted extraction with high-performance liquid chromatography for determination of andrographolide and dehydroandrographolide in Andrographis paniculata Nees, J. Chromatogr. A 1140 (2007) 71-77. [21] L. Chen, L. Ding, H. Zhang, J. Li, Y. Wang, X. Wang, C. Qu, H. Zhang, Dynamic microwave-assisted extraction coupled with on-line spectrophotometric determination of safflower yellow in Flos Carthami, Anal. Chim. Acta 580 (2006) 75-82. [22] L. Zhang, Z. Liu, Optimization and comparison of ultrasound/microwave assisted extraction (UMAE) and ultrasonic assisted extraction (UAE) of lycopene from tomatoes, Ultrason. Sonochem. 15 (2008) 731-737. [23] M. Larhed, A. Hallberg, Microwave-assisted high-speed chemistry: a new technique in drug discovery, Drug Discov. Today 6 (2001) 406-416. [24] L. Chen, Q. Zhao, Y. Xu, L. Sun, Q. Zeng, H. Xu, H. Wang, X. Zhang, A. Yu, H. Zhang, L. Ding, A green method using micellar system for determination of sulfonamides in soil, Talanta 82 (2010) 1186-1192. [25] R. Cueva-Mestanza, Z. Sosa-Ferrera, M.E. Torres-Padrón, J.J. Santana-Rodríguez, Preconcentration of pharmaceuticals residues in sediment samples using microwave assisted micellar extraction coupled with solid phase extraction and their determination by HPLC-UV, J. Chromatogr. B 863 (2008) 150-157. [26] V. Pino, J.H. Ayala, V. González, A.M. Afonso, Focused microwave-assisted micellar extraction combined with solid-phase microextraction gas chromatography/mass spectrometry to determine chlorophenols in wood samples, Anal. Chim. Acta 582 (2007) 10-18. 14 Page 14 of 23

[27] J.-f. Liu, J.Å. Jönsson, G.-b. Jiang, Application of ionic liquids in analytical chemistry, Trends Anal. Chem. 24 (2005) 20-27. [28] Z. Li, Y. Pei, H. Wang, J. Fan, J. Wang, Ionic liquid-based aqueous two-phase systems and their applications in green separation processes, Trends Anal. Chem. 29 (2010) 1336-1346. [29] M. Sturini, A. Speltini, F. Maraschi, E. Rivagli, A. Profumo, Solvent-free microwave-assisted extraction of fluoroquinolones from soil and liquid chromatography-fluorescence determination, J. Chromatogr. A 1217 (2010) 7316-7322. [30] E. Turiel, A. Martín-Esteban, J.L. Tadeo, Multiresidue analysis of quinolones and fluoroquinolones in soil by ultrasonic-assisted extraction in small columns and HPLC-UV, Anal. Chim. Acta 562 (2006) 30-35. [31] J. Dobor, M. Varga, J. Yao, H. Chen, G. Palkó, G. Záray, A new sample preparation method for determination of acidic drugs in sewage sludge applying microwave assisted solvent extraction followed by gas chromatography–mass spectrometry, Microchem. J. 94 (2010) 3641. [32] W. Song, Y. Zhang, G. Li, H. Chen, H. Wang, Q. Zhao, D. He, C. Zhao, L. Ding, A fast, simple and green method for the extraction of carbamate pesticides from rice by microwave assisted steam extraction coupled with solid phase extraction, Food Chem. 143 (2014) 192-198. [33] R. Fernandez-Torres, M.A.B. Lopez, M.O. Consentino, M.C. Mochon, M.R. Payan, Enzymatic-microwave assisted extraction and high-performance liquid chromatography–mass spectrometry for the determination of selected veterinary antibiotics in fish and mussel samples, J. Pharmaceut. Biomed. 54 (2011) 1146-1156. [34] L. Pareja, A.R. Fernández-Alba, V. Cesio, H. Heinzen, Analytical methods for pesticide residues in rice, Trends Anal. Chem. 30 (2011) 270-291. [35] Y.-F. Li, L.-Q. Qiao, F.-W. Li, Y. Ding, Z.-J. Yang, M.-L. Wang, Determination of multiple pesticides in fruits and vegetables using amodified quick, easy, cheap, effective, rugged and safe method withmagnetic nanoparticles and gas chromatography tandem massspectrometry, J. Chromatogr. A 1361 (2014) 77-87. [36] T.D. Nguyen, E.M. Han, M.S. Seo, S.R. Kim, M.Y. Yun, D.M. Lee, G.-H. Lee, A multi-residue method for the determination of 203 pesticides in rice paddies using gas chromatography/mass spectrometry, Anal. Chim. Acta 619 (2008) 67-74. [37] V. Guillet, C. Fave, M. Montury, Microwave/SPME method to quantify pesticide residues in tomato fruits, J. Environ. Sci. Heal. B 44 (2009) 415-422. [38] H. Wang, G. Li, Y. Zhang, H. Chen, Q. Zhao, W. Song, Y. Xu, H. Jin, L. Ding, Determination of triazine herbicides in cereals using dynamic microwave-assisted extraction with solidification of floating organic drop followed by high-performance liquid chromatography, J. Chromatogr. A 1233 (2012) 36- 43. [39] L. Wu, Y. Song, X. Xu, N. Li, M. Shao, H. Zhang, A. Yu, C. Yu, Q. Ma, C. Lu, Z. Wang, Medium-assisted non-polar solvent dynamic microwave extraction for determination of organophosphorus pesticides in cereals using gas chromatography-mass spectrometry, Food Chem. 162 (2014) 253-260. [40] T. Zhou, X. Xiao, G. Li, Microwave accelerated selective soxhlet extraction for the determination of organophosphorus and carbamate pesticides in ginseng with gas chromatography/mass spectrometry, Anal. Chem. 84 (2012) 5816-5822. [41] J. Wang, J. Xiong, G.A. Baker, R.D. JiJi, S.N. Baker, Developing microwave-assisted ionic liquid microextraction for the detection and tracking of hydrophobic pesticides in complex environmental matrices, RSC Adv. 3 (2013) 17113-17119. 15 Page 15 of 23

[42] E.-N. Papadakis, A. Kyrgidou, Z. Vryzas, E. Papadopoulou-Mourkidou, Development of a microwave-assisted extraction method for the determination of organochlorine pesticides in mussel tissue, Food Anal. Methods 7 (2014) 1271-1277. [43] Y. Zhang, N. Lin, S. Su, G. Shen, Y. Chen, C. Yang, W. Li, H. Shen, Y. Huang, H. Chen, X. Wang, W. Liu, S. Tao, Freeze drying reduces the extractability of organochlorine pesticides in fish muscle tissue by microwave-assisted method, Environ. Pollut. 191 (2014) 250-252. [44] Y. Merdassa, J.-f. Liu, N. Megersa, Development of a one-step microwave-assisted extraction method for simultaneous determination of organophosphorus pesticides and fungicides in soils by gas chromatography–mass spectrometry, Talanta 114 (2013) 227-234. [45] J. Raich-Montiu, M.D. Prat, M. Granados, Extraction and analysis of avermectines in agricultural soils by microwave assisted extraction and ultra high performance liquid chromatography coupled to tandem mass spectrometry, Anal. Chim. Acta 697 (2011) 32-37. [46] Y. Merdassa, J.-f. Liu, N. Megersa, Development of a one-step microwave-assisted extraction procedure for highly efficient extraction of multiclass fungicides in soils, Anal. Methods 6 (2014) 3025-3033. [47] Y.-S. Su, C.-T. Yan, V.K. Ponnusamy, J.-F. Jen, Novel solvent-free microwave-assisted extraction coupled with low-density solvent-based in-tube ultrasound-assisted emulsification microextraction for the fast analysis of organophosphorus pesticides in soils, J. Sep. Sci. 36 (2013) 2339-2347. [48] C. Coscollà, M. Castillo, A. Pastor, V. Yusà, Determination of 40 currently used pesticides in airborne particulate matter (PM 10) by microwave-assisted extraction and gas chromatography coupled to triple quadrupole mass spectrometry, Anal. Chim. Acta 693 (2011) 72-81. [49] D.V. Moreno, Z.S. Ferrera, J.J.S. Rodríguez, SPME and SPE comparative study for coupling with microwave-assisted micellar extraction in the analysis of organochlorine pesticides residues in seaweed samples, Microchem. J. 87 (2007) 139-146. [50] P.N. Carvalho, P.N.R. Rodrigues, F. Alves, R. Evangelista, M.C.P. Basto, M.T.S.D. Vasconcelos, An expeditious method for the determination of organochlorine pesticides residues in estuarine sediments using microwave assisted pre-extraction and automated headspace solid-phase microextraction coupled to gas chromatography–mass spectrometry, Talanta 76 (2008) 1124-1129. [51] H. Li, Y. Wei, J. You, M.J. Lydy, Analysis of sediment-associated insecticides using ultrasound assisted microwave extraction and gas chromatography–mass spectrometry, Talanta 83 (2010) 171-177. [52] S. Król, B. Zabiegała, J. Namieśnik, PBDEs in environmental samples: Sampling and analysis, Talanta 93 (2012) 1-17. [53] K.-H. Kim, S.A. Jahan, E. Kabir, R.J.C. Brown, A review of airborne polycyclic aromatic hydrocarbons (PAHs) and their human health effects, Environ. Int. 60 (2013) 71-80. [54] L.B.A. Mesa, J.M. Padró, M. Reta, Analysis of non-polar heterocyclic aromatic amines in beefburguers by using microwave-assisted extraction and dispersive liquid–ionic liquid microextraction, Food Chem. 141 (2013) 1694-1701. [55] M.I. Beser, J. Beltrán, V. Yusà, Design of experiment approach for the optimization of polybrominated diphenyl ethers determination in fine airborne particulate matter by microwave-assisted extraction and gas chromatography coupled to tandem mass spectrometry, J. Chromatogr. A 1323 (2014) 1-10. [56] L. Xu, H.K. Lee, Novel approach to microwave-assisted extraction and micro-solid-phase extraction from soil using graphite fibers as sorbent, J. Chromatogr. A 1192 (2008) 203-207. 16 Page 16 of 23

[57] J. Lv, R. Shi, Y. Cai, Y. Liu, Assessment of polycyclic aromatic hydrocarbons (PAHs) pollution in soil of suburban areas in Tianjin, China, Bull. Environ. Contam. Toxicol. 85 (2010) 5-9. [58] L. Guo, H.K. Lee, Microwave assisted extraction combined with solvent bar microextraction for one-step solvent-minimized extraction, cleanup and preconcentration of polycyclic aromatic hydrocarbons in soil samples, J. Chromatogr. A 1286 (2013) 9-15. [59] V. Pino, J.L. Anderson, J.H. Ayala, V. González, A.M. Afonso, The ionic liquid 1-hexadecyl-3-methylimidazolium bromide as novel extracting system for polycyclic aromatic hydrocarbons contained in sediments using focused microwave-assisted extraction, J. Chromatogr. A 1182 (2008) 145-152. [60] P. Sibiya, L. Chimuka, E. Cukrowska, H. Tutu, Development and application of microwave assisted extraction (MAE) for the extraction of five polycyclic aromatic hydrocarbons in sediment samples in Johannesburg area, South Africa, Environ. Monit. Assess. 185 (2013) 5537-5550. [61] V. Ghasemzadeh-Mohammadi, A. Mohammadi, M. Hashemi, R. Khaksar, P. Haratian, Microwave-assisted extraction and dispersive liquid–liquid microextraction followed by gas chromatography–mass spectrometry for isolation and determination of polycyclic aromatic hydrocarbons in smoked fish, J. Chromatogr. A 1237 (2012) 30-36. [62] X.-Y. Li, N. Li, H.-D. Luo, L.-R. Lin, Z.-X. Zou, Y.-Z. Jia, Y.-Q. Li, A novel synchronous fluorescence spectroscopic approach for the rapid determination of three polycyclic aromatic hydrocarbons in tea with simple microwave-assisted pretreatment of sample, J. Agric. Food Chem. 59 (2011) 5899-5905. [63] M. Germán-Hernández, V. Pino, J.L. Anderson, A.M. Afonso, Use of ionic liquid aggregates of 1-hexadecyl-3-butyl imidazolium bromide in a focused-microwave assisted extraction method followed by high-performance liquid chromatography with ultraviolet and fluorescence detection to determine the 15 + 1 EU priority PAHs in toasted cereals (“gofios”), Talanta 85 (2011) 1199-1206. [64] M. Germán-Hernández, V. Pino, J.L. Anderson, A.M. Afonso, A novel in situ preconcentration method with ionic liquid-based surfactants resulting in enhanced sensitivity for the extraction of polycyclic aromatic hydrocarbons from toasted cereals, J. Chromatogr. A 1227 (2012) 29-37. [65] M.D. Hernando, M. Mezcua, A.R. Fernández-Alba, D. Barceló, Environmental risk assessment of pharmaceutical residues in wastewater effluents, surface waters and sediments, Talanta 69 (2006) 334-342. [66] V. Gabet, C. Miège, P. Bados, M. Coquery, Analysis of estrogens in environmental matrices, Trends Anal. Chem. 26 (2007) 1113-1131. [67] H. Wang, Y. Xu, W. Song, Q. Zhao, X. Zhang, Q. Zeng, H. Chen, L. Ding, N. Ren, Automatic sample preparation of sulfonamide antibiotic residues in chicken breast muscle by using dynamic microwaveassisted extraction coupled with solid-phase extraction, J. Sep. Sci. 34 (2011) 2489-2497. [68] H. Wang, X. Zhou, Y. Zhang, H. Chen, G. Li, Y. Xu, Q. Zhao, W. Song, H. Jin, L. Ding, Dynamic microwave-assisted extraction coupled with salting-out liquid—Liquid Extraction for Determination of Steroid Hormones in Fish Tissues, J. Agric. Food Chem. 60 (2012) 10343-10351.

17 Page 17 of 23

[69] L. Chen, Q. Zeng, H. Wang, R. Su, Y. Xu, X. Zhang, A. Yu, H. Zhang, L. Ding, On-line coupling of dynamic microwave-assisted extraction to solid-phase extraction for the determination of sulfonamide antibiotics in soil, Anal. Chim. Acta 648 (2009) 200-206. [70] A. Azzouz, E. Ballesteros, Combined microwave-assisted extraction and continuous solid-phase extraction prior to gas chromatography–mass spectrometry determination of pharmaceuticals, personal care products and hormones in soils, sediments and sludge, Sci. Total Environ. 419 (2012) 208-215. [71] D. Matějíček, On-line two-dimensional liquid chromatography–tandem mass spectrometric determination of estrogens in sediments, J. Chromatogr. A 1218 (2011) 2292-2300. [72] K. Kotnik, T. Kosjek, U. Krajnc, E. Heath, Trace analysis of benzophenone-derived compounds in surface waters and sediments using solid-phase extraction and microwave assisted extraction followed by gas chromatography–mass spectrometry, Anal. Bioanal. Chem. 406 (2014) 3179-3190. [73] T. Vega-Morales, Z. Sosa-Ferrera, J.J. Santana-Rodríguez, Determination of various estradiol mimicking-compounds in sewage sludge by the combination of microwave-assisted extraction and LC–MS/MS, Talanta 85 (2011) 1825-1834. [74] S. Montesdeoca‐Esponda, Z. Sosa‐Ferrera, J.J. Santana‐Rodríguez, Combination of microwave assisted micellar extraction with liquid chromatography tandem mass spectrometry for the determination of fluoroquinolone antibiotics in coastal marine sediments and sewage sludges samples, Biomed. Chromatogr. 26 (2012) 33-40. [75] Y. Picó, Ultrasound-assisted extraction for food and environmental samples, Trends Anal. Chem. 43 (2013) 84-99. [76] P. Wang, Q. Zhang, Y. Wang, T. Wang, X. Li, L. Ding, G. Jiang, Evaluation of Soxhlet extraction, accelerated solvent extraction and microwave-assisted extraction for the determination of polychlorinated biphenyls and polybrominated diphenyl ethers in soil and fish samples, Anal. Chim. Acta 663 (2010) 43-48. [77] N. Dorival-García, A. Zafra-Gómez, F.J. Camino-Sánchez, A. Navalón, J.L. Vílchez, Analysis of quinolone antibiotic derivatives in sewage sludge samples by liquid chromatography–tandem mass spectrometry: Comparison of the efficiency of three extraction techniques, Talanta 106 (2013) 104-118. [78] N. Dorival-García, A. Zafra-Gómez, A. Navalón, J.L. Vílchez, Analysis of bisphenol A and its chlorinated derivatives in sewage sludge samples. Comparison of the efficiency of three extraction techniques, J. Chromatogr. A 1253 (2012) 1-10. [79] J.A. Pérez-Serradilla, F. Priego-Capote, M.D.L.d. Castro, Simultaneous ultrasound-assisted emulsification-extraction of polar and nonpolar compounds from solid plant samples, Anal. Chem. 79 (2007) 6767-6774. [80] H. Sun, N. Sun, H. Li, J. Zhang, Y. Yang, Development of multiresidue analysis for 21 synthetic colorants in meat by microwave-assisted extraction solid phase extraction reversed phase ultrahigh performance liquid chromatography, Food Anal. Methods 6 (2013) 1291-1299. [81] H. Sun, Y. Yang, H. Li, J. Zhang, N. Sun, Development of multiresidue analysis for twenty phthalate esters in edible vegetable oils by microwave-assisted extraction—gel permeation chromatography—solid phase extraction—gas chromatography-tandem mass spectrometry, J. Agric. Food Chem. 60 (2012) 5532-5539. [82] J. Wang, Z. Lin, K. Lin, C. Wang, W. Zhang, C. Cui, J. Lin, Q. Dong, C. Huang, Polybrominated diphenyl ethers in water, sediment, soil, and biological samples from different industrial areas in Zhejiang, China, J. Hazard. Mater. 197 (2011) 211- 219. 18 Page 18 of 23

[83] Á. Sánchez-Rodríguez, Z. Sosa-Ferrera, J.J. Santana-Rodríguez, Applicability of microwave-assisted extraction combined with LC–MS/MS in the evaluation of booster biocide levels in harbour sediments, Chemosphere 82 (2011) 96-102. [84] M. Förster, V. Laabs, M. Lamshöft, T. Pütz, W. Amelung, Analysis of aged sulfadiazine residues in soils using microwave extraction and liquid chromatography tandem mass spectrometry, Anal. Bioanal. Chem. 391 (2008) 1029-1038. [85] B. Wang, B. Huang, W. Jin, S. Zhao, F. Li, P. Hu, X. Pan, Occurrence, distribution, and sources of six phenolic endocrine disrupting chemicals in the 22 river estuaries around Dianchi Lake in China, Environ. Sci. Pollut. Res. 20 (2013) 3185-3194. [86] R. Wang, P. Su, Y. Yang, Optimization of ionic liquid-based microwave-assisted dispersive liquid–liquid microextraction for the determination of plasticizers in water by response surface methodology, Anal. Methods 5 (2013) 1033-1039. [87] Z. Gao, T. Liu, X. Yan, C. Sun, H. He, S. Yang, Application of ionic liquid-based microwave-assisted extraction of malachite green and crystal violet from water samples, J. Sep. Sci. 36 (2013) 1112-1118. [88] S. Montesdeoca-Esponda, Z. Sosa-Ferrera, J.J. Santana-Rodríguez, Microwave-assisted extraction combined with on-line solid phase extraction followed by ultra-high-performance liquid chromatography with tandem mass spectrometric determination of benzotriazole UV stabilizers in marine sediments and sewage sludges, J. Sep. Sci. 36 (2013) 781-788.

Captions Fig. 1. On-line microwave-assisted extraction (MAE) system. Fig. 2. Dynamic microwave-assisted extraction-solid-phase extraction (DMAE-SPE) system. (A) Mono-sample DMAE and (B) Multi-sample DMAE. Fig. 3. Microwave-assisted micellar extraction (MAME) procedure.

Table 1. Recent applications of microwave-assisted extraction (MAE) in food analysis Analytes

Sample matrix

PAHs

Fish

PMAE

Carbamates

Rice

MASE

Pesticide

Tomato

MAE modes

FMAE

Sample preparation MAE (20 min) → cooling→ filter → evaporation→ reconstitution MASE → on-line cooling→ SPE clean-up → elution

Triazines

Cereals

DMAE

Enrichment /

Volume

Volume

Acetonitrile / 10 mL



Water steam

MAE (5 min)→ centrifugation (3

Acetonitrile-water

min)→ SPME clean-up (30 or 45 min)

(1:1, v/v) or water

→ desorption (2 min) Multi-sample

Extractant /

DMAE (7 min)→ salt out→ centrifugation (3 min)→ cooling (5 min)

Detector

LC-FD

Acetonitrile/ 1 mL

Fiber

LC-MS/MS

GC–MS

/ 240 mL Methanol–water

1-dodecanol /

(1:9, v/v) / 10 mL

90 µL

HPLC

19 Page 19 of 23

Organophosphorus Cereals

Pesticides

Ginseng

Mono-sample DMAE

reconstitution

FMAE

MAE (15 min)→ evaporation

Almond milk, Pyrethroid

honey and

DMAE (200 s)→ evaporation→

PMAE

fruits

MAE (1 min)→ cooling→ centrifugation (10 min)

Hexane / 7 mL

Ethyl acetate / 30 mL

[N8881][Tf2N] / 20 µL

Hexane /

GC-MS

0.5 mL —

GC-MS

[N8881][Tf2N] / 20 µL

HPLC

MAE (10 min)→ cooling→ centrifugation (5 min) → Organochlorine

Mussel tissue

PMAE

evaporation→ reconstitution→ SPE

Acetonitrile / 40 mL

clean-up → elution→ evaporation→

Ethyl acetate/ 100 µL

GC-MS

reconstitution

Organochlorine

Fish

PMAE

MAE → cooling→ liquid-liquid extraction→ SPE clean-up → elution

Acetonitrile



GC-MS

MAE (15 min)→ vortex→ centrifugation (6 min)→ filter→ HAAs

Beefburger

PMAE

dispersive liquid–ionic liquid microextraction (mixture →

NaOH solution / 12 mL

[OMIM][BF4] and NaPF6 / 200 µL

HPLC

and 240 µL

centrifugation → dilution) MAE (2 min)→ cooling→ PAHs

Smoked fish

FMAE

centrifugation (5 min)→ adjustment of pH→ centrifugation (5 min)→ shake→ centrifugation (10 min) MAE (4 min)→ cooling→ filter→

PAHs

Tea

FMAE

dilution → liquid-liquid extraction→ evaporation→ reconstitution

PAHs

Toasted cereals

PMAE

MAE (14 min)→ cooling→ centrifugation (5 min)

KOH solution -ethyl alcohol (1:1, v/v)

C2Cl4 / 100 µL

GC–MS

/ 12 mL

Dimethyl sulfoxide / 15 mL

C16C4Im-Br aqueous solution / 4.5 mL



GC-MS



HPLC

MAE (14 min)→ cooling→

PAHs

Toasted cereals

centrifugation (5 min)→ filter→ PMAE

mixture→ vortex (2.5 min)→ centrifugation (4 min)→ freeze (1

C16C4Im-Br aqueous C16C4Im-NTf2 / solution / 4.5 mL

65 µL

HPLC

h)→ dilution

Sulfonamides

Steroid hormones

Chicken

Fish

Multi-sample DMAE Multi-sample DMAE

DMAE and on-line SPE clean-up (6 min)→ elution DMAE (10 min)→ salt out (6 min)→ evaporation→ reconstitution

Acetonitrile / 10 mL Acetonitrile (5 mL) and water (5 mL)



LC-MS/MS



LC-MS/MS

20 Page 20 of 23

MAE (5 min)→ cooling→ Synthetic Colorants

Meat

PMAE

centrifugation (3 min)→ SPE clean-up (about 12 min) →elution →

Methanol-water (95:5, v/v) / 15 mL



HPLC



GC-MS/MS

evaporation→ reconstitution MAE (15 min)→ cooling→ evaporation→ reconstitution→ Phthalate esters

Vegetable oils

PMAE

centrifugation (10 min)→ GPC clean-up→ evaporation→ SPE

Methanol / 5 mL

clean-up→ elution→ stand (15 min)→ evaporation→ reconstitution

Table 2. Recent applications of microwave-assisted extraction (MAE) in the analysis of environmental matrices Analytes

Pharmaceuticals

Pesticide and fungicide

Sample matrix

Sediment

Soil

MAE modes

PMAE

PMAE

Sample preparation MAME (6 min)→ cooling → filter → SPE clean-up→ vacuum dry (5 min)→ elution

Soil

PMAE

Soil

PMAE

Organophosphorus

Soil

FMAE

PM 10

PMAE

Detector

8 mL

HPLC

12 mL

GC–MS

6 mL

UHPLC–MS/M

Ethyl acetate

5 mL

HPLC

Water

5 mL

GC-µECD

Ethyl acetate

30 mL

GC–MS/MS

10 mL

HPLC

Polyoxyethylene 10 lauryl ether (5%, v/v) Acetone-hexane

filter→ evaporation→ reconstitution

(2:1,v/v)

(15 min)→ dilution→ filter→ SPE clean-up → rinse → elution

Fungicides

Volume

MAE (10 min)→ cooling (15 min)→

MAE (15 min)→ cooling→ centrifugation Avermectin

Extractant

MAE (15 min)→ cooling (15 min)→ filter→ evaporation→ reconstitution MAE (2.5 min)→ centrifugation (1 min)→ UAEME (30 s) → centrifugation (3 min)

Acetonitrile-water (90:10, v/v)

MAE (20 min)→ cooling→ evaporation→ Pesticides

reconstitution→ GPC clean-up→ evaporation → reconstitution MAME (14 min)→ cooling (15 min)→

Organochlorine

Seaweed

PMAE

filter → SPME clean-up (10 min)→ elution MAME (14 min)→ cooling (15 min)→ filter → SPE clean-up (6 min)→ elution

Organochlorine

Sediment

On-line MAE

MAE (6 min)→ cooling (15 min) → centrifugation→ headspace SPME (60 min)

Polyoxyethylene 10 lauryl ether (5%, v/v) GC–ECD Methanol

10 mL

GC–MS

21 Page 21 of 23

Insecticides

Sediment

UMAE with bath

UMAE (6 min)→ SPE clean-up→ evaporation

(1:1, v/v)

MAE (2 min)→ cooling→ evaporation→ PBDEs

PM 2.5

PMAE

reconstitution→ GPC clean-up (22 min)→ evaporation → reconstitution

PAHs

Soil

PMAE

Hexane-acetone

On-line MAE and µ-SPE (20 min)→ cooling (10 min)→ elution (5 min)

Acetone-hexane (1:1, v:v)

Water

100 mL

GC-MS

50 mL

GC-MS/MS

GC–FID

10 mL

GC–MS

MAE (60 min)→ centrifugation (10 min)→ PAHs

Soil

PMAE

dilution→ SPE clean-up→ elution→

PAHs

Soil

PMAE

On-line MAE and SBPE → cooling

PAHs

Sediment

PMAE

MAE (6 min)→ cooling (20 min)→ filter

Soil

30 mL

GC-MS

Water

10 mL

GC-MS

HDMIm-Br

405 µL

LC-FD

Acetonitrile

12 mL

LC-MS/MS

10 mL

GC-MS

10 mL

LC–MS/MS

30 mL

GC-MS

5 mL

LC–MS/MS

15 mL

LC-MS/MS

20 mL

GC-MS

Methanol

10 mL

LC–MS/MS

Acetonitrile-water

50 mL

HPLC–MS/MS

(1:1, v:v)

evaporation

Sulfonamides

Acetone-hexane

Mono-sample DMAE (15 min)→ SPE clean-up→ rinse (2 min)→ elution (1.5 min) DMAE MAE (6 min)→ evaporation→

Pharmaceuticals and hormones

Soil, sediments and sludge

reconstitution → SPE clean-up (3 min)→ On-line MAE

elution→ concentration→ derivatization

Methanol-water (3:2, v/v)

(20 min) MAE (10 min)→ cooling→ filter→ Estrogens

Sediments

PMAE

evaporation→ reconstitution

Methanol-water (95:5, v/v)

MAE (30 min)→ cooling→ centrifugation (20 min, twice)→ evaporation→ Benzophenone derived compounds

Sediments

PMAE

reconstitution→ SPE clean-up → elution→ evaporation→ reconstitution→ derivatization (1 h)

Sewage sludge

PMAE

5 % (w/w) formic acid

filter→ dilution (5 min)→ filter→ SPE

Methanol

clean-up → rinse → elution

compounds Marine Fluoroquinolone

(1:1, v/v) with

MAE (10 min)→ cooling (20 min)→

Estradiol mimicking

Methanol-acetone

sediments and

PMAE

sewage sludges

MAME (15 min)→ cooling (20 min)→ filter

Hexadecyltrimeth ylammonium bromide(5%, v/v)

MAE (20 min)→ sonication (30 min)→ Polybrominated diphenyl ethers

Soil and sediment

PMAE

filter → concentration→ reconstitution→

Hexane-acetone

SPE clean-up→ elution→ evaporation→

(1:1, v/v)

reconstitution

Booster biocide Sulfadiazine

Harbor sediments Soil

MAE (6 min)→ cooling (20 min)→ SPE PMAE

clean-up → rinse → elution

PMAE

MAE (15 min) 22

Page 22 of 23

(1:4, v/v) MAE (20 min)→ dilution→ reconstitution → GPC clean-up→ evaporation→

Endocrine disrupting

Sediment

reconstitution→ SPE clean-up→ rinse→

PMAE

Methanol

25 mL

GC-MS

[BMIM][PF6]

100 µL

HPLC

[C8MIM][PF6]

500 µL

HPLC

Acetonitrile

2 mL

UHPLC–MS/M

elution→ evaporation→ derivatization (20

compounds

min)

Plasticizers

Water

PMAE

Water

PMAE

MAE (3 min)→ cooling→ centrifugation (3 min)

Malachite green and crystal

MAE (2 min)→ cooling→ centrifugation (5 min) → dilution

violet Benzotriazole

Marine

ultra-violet

sediments and

stabilizers

sewage sludges

MAE (5 min)→ cooling (20 min)→online

On-line

SPE clean-up (load→ rinse→ elution)

MAE

Table 3. Analytical figures of merit of extraction techniques SE

UAE

PMAE

12 or 24 h

10×2 min

10-20 min

150-250

5-10

10-30

12 or 24 h

90-100 min

50-75 min

40-65

Operator skill

Low

Moderate

Moderate

Mode

Simultaneous



up to 4 samples can be extracted simultaneously

up to 10 vessels can be extracted simultaneously



Low

Moderate

High

Hig



Low

High

Mode

Extraction time Solvent consumption (mL ) Pretreatment time

Recovery

PLE

5×5 m

15

Matrix effects (signal suppression)

23 Page 23 of 23