Ultrasound-assisted extraction for food and environmental samples Yolanda Pico ´ In recent years, ultrasound-assisted extraction (UAE) has attracted growing interest, as it is an effective method for the rapid extraction of a number of compounds from food and environmental samples, with extraction efficiency comparable to that of classical techniques. In particular, recently, numerous analytical applications of this technique dealt with the extraction of natural compounds and pollutants from food and environmental samples. This review gives a brief presentation of the theory of UAE, discusses recent advances that influence its efficiency, and summarizes the main results in selected applications published in the period 2010–12. There is discussion of the advantages and the disadvantages of UAE and the possibility of coupling UAE with other analytical techniques. ª 2012 Elsevier Ltd. All rights reserved. Keywords: Analytical application; Contaminant; Environmental matrix; Environmental sample; Extraction; Food sample; Natural compound; Pollutant; Ultrasound-assisted extraction (UAE); Ultrasound-assisted emulsification microextraction (UAEME) 1. Introduction For many years, the use of ultrasound energy in liquid and solid media has been extensive in food-processing applications and has created growing interest in sam- ple treatment [1]. This technique is an efficient tool for large-scale commercial applications (e.g., emulsification, homog- enization, extraction, crystallization, dewatering, low-temperature pasteuriza- tion, degassing, defoaming, activation and inactivation of enzymes, particle-size reduction and changing viscosity) [2,3]. Much attention has been given to the application of ultrasound for the extrac- tion of natural products that typically needed hours or days to reach completion with conventional methods [3–7]. The classical techniques used in food industry for solvent extraction of bioactive compounds are based upon the correct choice of solvent coupled with the use of heat and/or agitation. Solvent extraction of organic compounds contained within the bodies of plants and seeds is signifi- cantly improved by using the power of ultrasound. The mechanical effects of ultrasound provide a greater solvent pen- etration into cellular materials and im- prove mass transfer due to the effects of micro-streaming. This is combined with an additional benefit of using ultrasound in extractive processes – disruption of biological cell walls to release the cell contents [8]. Overall, ultrasound-assisted extraction (UAE) is recognized as an efficient extrac- tion technique that dramatically reduces working times, increasing yields and often the quality of the extract [8]. Several studies have reviewed different industrial applications of ultrasound in the intensi- fication of extraction of bioactive materials from herbs, oils from seeds and proteins from soy [9–11]. Thus, in the past few years, numerous compounds have been extracted by UAE from several matrices, with special emphasis on the commercial production of bioactive compounds in the food industry. UAE is also gradually becoming a mat- ter of routine practice in analytical chemistry, which uses this energy for a variety of purposes in relation to sample preparation, mostly sample extraction. Currently, any critical review of recent advances in sample preparation includes a section dedicated to UAE [12–17]. Over 80% of analysis time is still spent on the sample and sample preparation, and UAE can speed up many procedures that are appropriate in other respects [12,15,17]. There were recently some review articles about UAE [4] and its applications to microwave [18], lesser known Yolanda Pico ´* Food and Environmental Safety Research Group, Department of Medicine Preventive, Facultat de Farma `cia, Universitat de Vale `ncia, Av. Vicent Andre ´s Estelle ´s s/n, 46100 Burjassot, Vale `ncia, Spain * Tel.: +34 96 3543092; Fax: +34 96 3544954; E-mail: [email protected]Trends Trends in Analytical Chemistry, Vol. 43, 2013 84 0165-9936/$ - see front matter ª 2012 Elsevier Ltd. All rights reserved. doi:http://dx.doi.org/10.1016/j.trac.2012.12.005
Transcript
Trends Trends in Analytical Chemistry, Vol. 43, 2013
Ultrasound-assisted extraction forfood and environmental samplesYolanda Pico
In recent years, ultrasound-assisted extraction (UAE) has attracted growing interest, as it is an effective method for the rapid
extraction of a number of compounds from food and environmental samples, with extraction efficiency comparable to that of
classical techniques. In particular, recently, numerous analytical applications of this technique dealt with the extraction of
natural compounds and pollutants from food and environmental samples.
This review gives a brief presentation of the theory of UAE, discusses recent advances that influence its efficiency, and
summarizes the main results in selected applications published in the period 2010–12. There is discussion of the advantages and
the disadvantages of UAE and the possibility of coupling UAE with other analytical techniques.
For many years, the use of ultrasoundenergy in liquid and solid media has beenextensive in food-processing applicationsand has created growing interest in sam-ple treatment [1]. This technique is anefficient tool for large-scale commercialapplications (e.g., emulsification, homog-enization, extraction, crystallization,dewatering, low-temperature pasteuriza-tion, degassing, defoaming, activation andinactivation of enzymes, particle-sizereduction and changing viscosity) [2,3].Much attention has been given to theapplication of ultrasound for the extrac-tion of natural products that typicallyneeded hours or days to reach completionwith conventional methods [3–7].
The classical techniques used in foodindustry for solvent extraction of bioactivecompounds are based upon the correctchoice of solvent coupled with the use ofheat and/or agitation. Solvent extractionof organic compounds contained withinthe bodies of plants and seeds is signifi-cantly improved by using the power ofultrasound. The mechanical effects ofultrasound provide a greater solvent pen-etration into cellular materials and im-prove mass transfer due to the effects ofmicro-streaming. This is combined withan additional benefit of using ultrasound
0165-9936/$ - see front matter ª 2012 Elsevier Ltd. All rights
in extractive processes – disruption ofbiological cell walls to release the cellcontents [8].
Overall, ultrasound-assisted extraction(UAE) is recognized as an efficient extrac-tion technique that dramatically reducesworking times, increasing yields and oftenthe quality of the extract [8]. Severalstudies have reviewed different industrialapplications of ultrasound in the intensi-fication of extraction of bioactive materialsfrom herbs, oils from seeds and proteinsfrom soy [9–11]. Thus, in the past fewyears, numerous compounds have beenextracted by UAE from several matrices,with special emphasis on the commercialproduction of bioactive compounds in thefood industry.
UAE is also gradually becoming a mat-ter of routine practice in analyticalchemistry, which uses this energy for avariety of purposes in relation to samplepreparation, mostly sample extraction.Currently, any critical review of recentadvances in sample preparation includes asection dedicated to UAE [12–17]. Over80% of analysis time is still spent on thesample and sample preparation, and UAEcan speed up many procedures that areappropriate in other respects [12,15,17].
There were recently some reviewarticles about UAE [4] and its applicationsto microwave [18], lesser known
Trends in Analytical Chemistry, Vol. 43, 2013 Trends
heterogeneous sample-preparation procedures [19] andgreen chemistry [20], and the determination of heavymetals [21] and organic food contaminants [22].
But, to the best of our knowledge, there is no singlereview that addresses the UAE applications to extractany type of compound in food and environmentalmatrices. Consequently, this article reviews the applica-tion of ultrasound energy to the extraction of organic,organometallic and inorganic compounds from envi-ronmental and food matrices (soils, sediments, vegeta-bles, animal tissues, and water) for their analyticaldetermination. The principle of the technique is firstpresented, together with the commercially availablesystems. Then, the main parameters and operations arediscussed, before the presentation of the experimentalconditions that allow the extraction of numerous com-pounds. The aim of this review is to describe differentaspects of recent interesting applications of UAE pub-lished since 2010. Finally, the performance of the tech-nique is compared to that of other techniques, eitherclassical or recent.
2. Principles of ultrasound extraction
Ultrasound comprises mechanical waves that need anelastic medium to spread. The difference between soundand ultrasound is the frequency of the wave; soundwaves are at human hearing frequencies (16 Hz to 16–20 kHz) while ultrasound has frequencies above humanhearing but below microwave frequencies (from 20 kHzto 10 MHz). For the classification of ultrasound appli-cations, the amount of energy generated, characterizedby sound power (W), sound intensity (W/m2) or soundenergy density (W/m3), is the key criterion. The uses ofultrasound are broadly distinguished into two groups:high intensity and low intensity [11,23,24].
Low-intensity ultrasound – high frequency (100 kHz–1 MHz) low power (typically <1 W/cm2) – is involved innon-destructive analysis, particularly for quality assess-ment. This technique is most commonly applied as ananalytical technique to provide information on thephysicochemical properties of food (e.g., firmness, ripe-ness, sugar content, and acidity). Nevertheless, high-intensity ultrasound – low frequency (16–100 kHz) highpower (typically 10–1000 W/cm2) – can alter foodproperties physically or chemically [8,9,23]. High-intensity ultrasound is used, among other applications,to speed up and to improve the efficiency of samplepreparation.
2.1. Effects of ultrasoundDuring the sonication process, longitudinal waves arecreated when a sonic wave meets a liquid medium,thereby creating regions of alternating compression andrarefaction waves induced on the molecules of the
medium (Fig. 1) [11]. In these regions of changingpressure, cavitation occurs and gas bubbles are formed.These bubbles have a larger surface area during therarefaction (expansion) cycle, which increases the dif-fusion of gas, causing the bubble to expand. A criticalpoint is reached during the compression cycle in whichthe ultrasonic energy provided is not sufficient to retainthe vapor phase in the bubble. As a consequence, rapidcondensation occurs and large amounts of energy arereleased [11,23,24]. The condensed molecules collideviolently, creating shock waves. These shock wavescreate regions of very high temperature and pressure,reaching up to 5500�C and 50 MPa [11,24]. Cavitationcan result in micro-streaming, which can enhance heatand mass transfer. This creates hotspots that can dra-matically accelerate the chemical reactivity in the med-ium. When these bubbles collapse onto the surface of asolid material, the high pressure and temperature re-leased generate microjets directed towards the solidsurface. These microjets are responsible for the degre-asing effect of ultrasound on metallic surfaces, which iswidely used for cleaning materials [8,9].
Another application of microjets in food industry is theextraction of vegetal compounds, because this allowsimproved solvent penetration into the plant body andcan also break down cell walls [11]. As shown in Fig. 2,a cavitation bubble can be generated close to the plantmaterial surface (a), then, during a compression cycle,this bubble collapses (b) and a microjet directed towardthe plant matrix is created (b and c). The high pressureand temperature involved in this process destroy the cellwalls of the plant matrix, and its content can be releasedinto the medium (d). This is a very interesting tool forextraction of ingredients from natural products [24]. Asa consequence, employing UAE has benefits in increasedmass transfer, better solvent penetration, less depen-dence on solvent use, extraction at lower temperatures,faster extraction rates and greater yields of product[11,23,24].
The ability of ultrasound to cause cavitation dependson the characteristics of ultrasound (e.g., frequency andintensity), product properties (e.g., viscosity and surfacetension) and ambient conditions (e.g., temperature andpressure). This technique requires a liquid medium, anenergy generator and a transducer, which transformsthe electric, magnetic or kinetic energy into acousticenergy [23].
2.2. Commercial devicesUltrasonication can be applied in analytical chemistry intwo ways: directly to the sample, or indirectly throughthe walls of the sample container using a water bath,which is the most available and cheapest source ofultrasound irradiation. However, there are other moreefficient designs [e.g., horns (indirect or direct) or ultra-sonic probes (direct to the sample)] able to develop
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Figure 1. Ultrasonic cavitation (reproduced with permission from [11]).
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higher ultrasound power. Fig. 3 shows several of thesecommercially available devices.
The ultrasonic bath that transmits high-energy andhigh-frequency sound waves into a fluid-filled container(commonly water), which is found in the chemical lab-oratories, is not a powerful tool. The irradiation power
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given by a common ultrasonic bath is 1–5 W/cm2 [25].The classic bath works with only one frequency, gener-ally 40 kHz, and can be supplied with temperaturecontrol [26–29]. Currently, there are different types ofbath provided with multi-frequency units, which operatesimultaneously ultrasonic transducers with different
Figure 2. Cavitation-bubble collapsing and releasing plant material: example of extraction of essential oil from basil (reproduced with permissionfrom [24]).
Figure 3. Advances on ultrasonic probe technology: (a) silica-glass probe; (b) spiral probe; (c) dual probe; (d) multi-probe; (e) cup horns; (f)sonoreactor; (g) microplate horns. {(a–d) are reproduced with permission of Bandelin Co [Berlin, Germany]; (e) and (g) are reproduced with per-mission of Misonix Co. [Farmingdale, NY, USA]; (e) is reproduced with permission of Dr. Hielscher Co. [Teltow, Germany]} (Reproduced withpermission from [25]).
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frequencies. Constant power and automatic frequencycontrol ensure optimal distribution of ultrasonic energy[26,27].
The ultrasonic probe (Fig. 3a–d) is immersed directlyinto the solution and provides an ultrasonic power thatis at least up to 100 times greater than that supplied bythe bath, with sonication time usually 5 min or less. Theprobe is a powerful system for solid-liquid extraction(SLE) of analytes that can be extracted but can also bedegraded. It should be stressed that the amplitude con-trol of the probes allows the ultrasonic vibrations at theprobe tip to be set to any desired level. However, toachieve cavitation, normally it is not necessary to usehigh amplitudes; otherwise, the probe will deterioraterapidly. Temperature is another factor that must becontrolled. As the ultrasound is delivered into the solu-tion, a slow but constant increase in the bulk tempera-ture is achieved, and, at some point, the physicalcharacteristics of the liquid media change so that theprobe can decouple and no more cavitation is achieved[30]. Ultrasonic probes have been used to extract traceand major inorganic acids from dust [31] and biologicalmatrices [32], to perform sugar profiling in oil [33], toextract biomarkers for fish identification [34] and toobtain peptide mapping of soybeans [35].
Indirect sonication means that the ultrasonic wavesneed to cross the wall of the sample container. This doesnot occur with the ultrasonic probe, which is directlyimmersed in the sample, giving direct in-sample soni-cation. Cup horns and sonoreactors can be compared tohigh-intensity ultrasonic water baths. As an example,the sonoreactor is 50 times more intense than anultrasonic bath. Samples can be processed in sealed tubesor vials, eliminating aerosols and cross-contamination.The ultrasonic horn has been successfully used for theextraction of metals from biological tissues [32] and goldand silver from sediments [36].
The choice of approach also depends on therequirements of the particular analysis. If the aim is totalSLE, the use of a powerful probe could be better, becauseless time is necessary for extraction. However, when agreat number of samples needs to be analyzed, the bathis the better option, because it allows simultaneousextraction of a number of samples, whereas the otherdevices can only process one sample at a time. Forexample, the ability of a classic sonication bath and ahorn inserted directly into the sample (thorn) to destroycell walls and liberate isoflavones were compared [37].The intensity of sonication was given by parameters ofthe sonic bath and could not be changed. Pretreatmentwas carried out for 30 min. The horn – a tapering metalbar commonly used to augment the oscillationdisplacement amplitude provided by an ultrasonictransducer – could adjust the intensity of sonication. Therequired process of matrix cell-wall destruction occurred(with measurable implications) at �60% of the
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instrument maximum performance. The original aim ofusing this device was to shorten the pretreatment time –more efficient sonication should do the job more quickly.However, the erosion of plant cell walls is a slow processin both modes. Sonication for 15 min was not enough,and at 30 min the results were comparable with treat-ment in a sonication bath. The interesting result was thefurther increase in isoflavone recovery with longer pre-treatment time, which was not observed with the soni-cation bath. Thus, although the thorn device was morelabor-intensive, there was a risk of the loss of analytes inthe open system and only one sample could be processedsimultaneously, the recoveries obtained this way wereeven better at the cost of even longer time of pretreat-ment.
With respect to different devices, two ultrasound-basedprocedures (i.e., UAE with a cup-horn sonoreactor andultrasonic-probe slurry sampling) were recently com-pared as sample pretreatments for the determination ofP, K, Ca, Cr, Mn, Fe, Ni, Cu, Zn, As, Se and Sr in differentbiological tissues (certified reference materials and realsamples) [32]. The cup-horn sonoreactor provided thebetter results and obtained quantitative extractionrecoveries for almost all elements. Consequently, it wasefficient for metal extraction in conjunction with severalextractant media. The versatility in the use of any acidand oxidant along with short sonication times and theability to carry out simultaneous extractions from sev-eral samples made the cup-horn sonoreactor moreadvantageous than probe and bath sonication systems.
3. Main applications
UAE of pollutants from environmental matrices has at-tracted considerable interest in the past few years. Ta-ble 1 shows applications of these techniques for thedetermination of natural products, food additives andcontaminants in food samples. Table 2 shows the re-ported applications of UAE to contaminant extractionfrom environmental matrices.
Sonication is used in sample preparation to assist thetreatment of solid samples, in the extraction, digestionand slurry formation, and in liquid sample preparationto assist liquid–liquid extraction (LLE), homogenizationor emulsification. Ultrasound extraction can be subdi-vided into UAE and ultrasound-assisted emulsificationmicroextraction (UAEME).
3.1. Ultrasound-assisted extraction (UAE)After interaction with subjected biological or non-bio-logical material, ultrasound waves alter their physicaland chemical properties and their cavitational effectfacilitates the release of extractable compounds andenhances the mass transport by disrupting membranes,plant cells walls and other structures. The most
Table 1. Recent applications of ultrasound-assisted extraction (UAE) in food analysis
Matrix Analytes Remarks on the extraction Recovery EF Determination LODs, ng/g Ref
Inorganic elementsSeafood Hg speciation UAE (0.2 g) with 10 mL of a mixture of
mercaptoethanol, l-cysteine and HCl for 15 minin an ultrasonic bath
90–94 – LC-ICP-MS Hg, 0.25HgCH2H3,.20HgCH3,0.1
[38]
Fish Hg speciation UAE (100 mg) with 4 mL of 5 M HCl for 15 min inan ultrasonic bath
– – GC-ICP-MS – [39]
Wheat grain Se UAEE (0.1 g) with a-amylase + 2 mL H2O for 60 sat 30 W and with protease for 60 s at 30 W by anultrasonic probe
70�90 – LC-ICP-MS – [30]
Cereals Se, Te UAE with H2SO4 and EDTA-Na2 for 10 min in anultrasonic bath
>90 – HG AFS 0.1–0.5 [40]
Additives and contaminantsCake, soy sauce, vinegar, jam,ham, beverage, pickle and beanpaste
Preservatives (11compounds)
UAEME (0.5 g + 25 mL water) fi 1 mL adjusted topH 3 + NaCl with 100 lL dichloromethane andethyl acetate (9:1) for 3 min in an ultrasonic bath
90.5–104.6 88–141 GC-MS 0.025–1.53 [41]
Sausage Sudan dyes MISPE-UAEME. (1 g) MISPE elution with 4 mLacetone–acetic acid (95:5, v/v), concentrated to1 mL. Then, UAEME is performed using 100 lL oftetrachloroethylene + 5 mL H2O for 2 min in anultrasonic bath
86.3–107.5 50 LC-UV 0.001–0.005 mg/g
[42]
Spices Fat-soluble dyes UAE (1 g) with 10 mL acetone-acetonitrile(50/50)for 15 min in an ultrasonic bath
92–109 – LC-UV 0.5–1 lg/g [43]
Wine 2,4,6-Trichloroanisole UAEME (5 mL) with 25 lL of trichloroethene for5 min at 20� C in an ultrasonic bath
>80 400 GC-MS/MS 0.6-0.7 ng/L [44]
Beverages Bisphenol A UAEME-ISD with ammonia buffer + aceticanhydride + chlorofom for 10 min at 50 � C in a40 kHz and 600 W ultrasonic bath withtemperature control
P 82 3 GC-MS 38 ng/L [45]
Muscle and liver of swine andchicken and in muscle of fish
Nitrovin and sodiumnifurstyrenate
UAE (5 g) with 10 mL of acetonitrile in anultrasonic bath (power: 100 W, frequency:40 kHz). Then, clean-up by SPE with Oasis HLBand elution with 1% DMF–methanol. Comparisonwith shaken extraction
71–110 10 LC-MS/MS 0.09–0.26 lg/kg [27]
Fish and mussels samples Antibacterials UAEE (1 g) with 5 mL of water and Proteinase-KSonicated for 5 min at 50% of the maximum
power of the ultrasounds probe (2200 W). Then,liquid-liquid extraction with dichloromethane.
53–83 2 LC-DAD andLC-FLD
0.11–0.45 lg/g [46]
Infant formula milk powder Sulfonamides UA-IL/IL-DLLME 4 mL of a mixture powder milk-water (1:8) using 70 lL of[C6MIM] [PF6] asextraction solvent + 100 lL of [C4MIM][BF4] asdisperser solvent. Then, 80 mg of NH4PF6 wereused as ion-pairing agent for the sedimentation ofIL cations. The mixture was extracted for 5 min at35 �C in an ultrasonic bath.
90.4–114.8 5 LC-DAD 2.64–6.66 ng/g [47]
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Table 1 (continued)
Matrix Analytes Remarks on the extraction Recovery EF Determination LODs, ng/g Ref
Fruit and juice sample Strobilurin and oxazolefungicides
LDS-UAEME (1 g + 0.4 g (10% m/v) sodiumchloride, 1 mL of 0.1 M phosphate buffer(pH 5)and water up to 4 mL) with 20 lL of undecanonefor 4 min at 25 �C in an ultrasonic bath(50 Hz and110 W) Comparison with SDME
80–119 140–1140 GC-MS (SIM) 0.006–0.075ng/mL
[48]
Cereal-based baby food Organophosphoruspesticides and somemetabolites
UAE (1.5 g) with20 mL 1 % formic acid inacetonitrile for 5 min in an ultrasonic bath(50/60 Hz and 100 W). Then, followed by dSPE withMWCNTs.
64–105 – GC-NPD 0.31–5.50 ng/g [49]
Tomato Organophosphoruspesticides
UAE (1.0 g) with 5.0 mL of acetone for 35 min inan ultrasonic bath. Followed by DLLME clean-up.
– 150 GC-FPD 0.1-0.5 lg/kg [50]
Palm oil Pesticides LLE and followed by low temperature oil frozen.Then, UAE-MSPD with PSA as dispersing agentand GBC as clean-up sorbent extracted with15 mL of acetonitrile for 15 min at roomtemperature in an ultrasonic bath
73–91 10 LC-TOF-MS 1.5–5 lg/kg [51]
Honey Pyrethroid pesticides UA-IL-DLLME (10 g + 100 mL H2O) fi 10 mL ofhomogeneous sample solution plus 60 lLC8MIM][PF6] dissolved in 200 lL methanol for2 min in an ultrasonic bathComparison with conventional IL-DLLME and TC-DLLME
101–103 506–515 LC-DAD UV 0.2–0.4 lg/L [52]
Natural productsBud of Citrus aurantium L. var.amara Engl.
Essential oils UAE with ethyl acetate (solid/liquid [/v] = 1:8) for20 min at 25 �C in an ultrasonic bath (100 W)Comparison with SDS and RE
GC-MS – [53]
Seed oil of MicroulasikkimensisHemsl.
Saturated andunsaturated fatty acids
UAE (5 g) with 25 mL of chloroform for 60 min inan ultrasonic bath followed by saponification ofthe oil.Comparison with SFE, MWRE and RE
91–105 7.35 LC-FLD after pre-columnderivatization withTSPP
3.2–37 fmol [54]
Olea europaea Sugar profiling UAE(100 mg) with 6.5 mL of a mixture ofmethanol-dichloromethane for a 10 min in anultrasonic probe (duty cycle = 0.5 s, outputamplitude = 60% of the converter, appliedpower = 450 W with the probe placed 1 cm fromthe bottom of the container)
– – Silylation GC-MS/MS
0.02–2 lg/mL [33]
Sea and freshwater algae andcyanobacteria
Isoflavones US-pretreatment (0.1 g) with 300 lL of SFEmodifier mixture (methanol:H2O 1:9, v/v)for30 min in ultrasonic bath or by the means of thethorn sonication device followed by SFE.Two different approaches of sonicationpretreatment were tested: sonication bath and thehorn instrument
94–103 – ULC-MS/MS 0.06–2 lg/L [37]
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Legumes Isoflavones UAE (10 g) with 10 mL of methanol for 2 h atroom temperature in an ultrasonic bath (40 kHz,135 W)
– – LC-MS/MS – [26]
Nightshades vegetal andcommercial food products
Nicotine UA-HF-LPME was performed using 5 lL oftoluene as an extracting solvent in 1.0 cm ofhollow fiber for 10 min in an ultrasonic bathComparison with DDSME
94–99 19 GC-MS 0.2–0.5 ng/g [55]
Fructus Corni Identification ofsubstances
UAME (0.5 g) with concentration of ethanol 70%,solvent-to-material ratio 24 ml/g; temperature,61�C and irradiation time 6.5 min. Simultaneousultrasound and microwave power
97–103 – LC-DAD UV 0.02-0.24 lg/mL [56]
Peptides/BiomarkersFish authentication Peptide biomarker After protein extraction with a Tris buffer, HIFU of
the PRVBs, considered as the best proteinbiomarker for the authentication of Merluciidaespecies, with trypsin. A high-intensity ultrasonicprobe with a 1 mm probe tip was set to 50%amplitude and was used to perform the ultrafastdigestion for 1 min.
– – LC-MS/MS – [34]
Soybean Peptide mapping UAE (600 mg of powdered soybean) with 10 mLof 50 mM Tris–HCl (pH 8.0) and 8 M urea. Theextraction was carried out for 3 min in anultrasonic bath. UAEE with trypsin in 1 min usingthe ultrasonic probe at 20% amplitude andwithout pulses.
Table 2. Some representative examples of the use of ultrasound-assisted extraction (UAE) in the analysis of environmental matrices.
Matrix Analytes Remarks on the extraction Recovery EF Determination LODs Ref
Inorganic elementsStreet dust samples Trace and major
elementsUAE (15 mg) with 1 mL concentrated HNO3-HCl (1:3,v/v) for 3 min by a 1 mm diameter titanium ultrasonicprobe (200 W, 24 kHz at 80% amplitude).
85–125 – ICP-MS 0.01–0.09 mg/kg [31]
Water Lead UAEME with 45 lL CCl4 and dithizone as complexingagent for 8 min in an ultrasonic bath (40 kHz, 100 W)
– 70 GFAAS 20 pg/mL [28]
Water Copper IUSA-DLLME and UAEME with 282 lL CCl4 anddiethyl-dithiocarbamate for 45 s in an ultrasonic bathComparison with LLE and injection-assisted DLLME
– 220 UV-Vis spectrometry 0.05 ng/mL [57]
Soil and water Te (IV) UAE-SFODME (14.0 mL)into the fine droplets of40.0 lL 1-undecanol after chelate formationammonium pyrrolidine dithiocarbamate for 4 min inan ultrasonic bath
97–106 342 GFAAS 3 ng/L [58]
Soil, sediment, fly ashand industrial sludge
Silver and gold UAE (3–30 mg)Two different systems(i) 1 mL of acid mixtures (HCl, HF, HNO3)(ii) 1 mL if thiourea in diluted H2SO4
Biological tissues P, K, Ca, Cr, Mn, Fe, Ni,Cu, Zn, As, Se and Sr
UAE (10 mg) with 1 mL of 0.01% w/v Triton X-100 + 3% v/v HNO3 using an ultrasonic-probe (30 s atan amplitude of 30%) or a cup-horn sonoreactor.Comparison of ultrasonic-probe and cup-hornsonoreactor with magnetic agitation
72–110 – Total reflection X-ray fluorescencespectrometry
0.9–187 lg/g [32]
Organic contaminantsIndoor dust Brominate and
organophosphate flameretardants
UAE (75 mg) with 2 mL hexane–Acetone (3:1, v/v) for5 min in an ultrasonic bath. Clean-up by fractionationin Florisil.
80–110 – GC-MS 0.04–17 ng/g [59]
Indoor air Fragrance allergens Retention of the target compounds on Florisil and UAE(25 mg) with ethyl acetate for 5 min using anultrasound bath at 40kHz of ultrasound frequency and200W power
>80 – GC-MS 60.6 lg/m3 [60]
House dust PBDE UAE (3 g) with 100 mL toluene for 2 h (eight 15-mincycles) with an ultrasonic bathComparison with PLE and Soxhlet
50–105 – GC-MSGC-ECD
– [61]
Groundwater samples Quinolones IL-UAEME (10 mL + 1.0% aqueous ammonia to pH 9)with 0.4 mL of methanol (disperser solvent) containing65 mg of [C8MIM] [PF6] (extraction solvent) for 5 minin an ultrasonic bath
85–107 122–205 LC-FLD 0.8- 13 ng/L [62]
Water Chlorinatedphenoxyacetic
UAEME (15 mL) with 240 lL of dichloromethane for5 min in an ultrasonic bath
95–113 22–83 LC-DAD 0.67-1.50 ng/mL [63]
Water Organochlorinepesticides
UAEME (10 mL + 0.2 g NaCl) with 10 lL of 1-decanolfor 4 min in an ultrasonic bath
70–107 1202–4587 GC-ECD 0.6 to 2.9 ng/L [64]
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Water BTEXs UAEME (10 mL) with 15 lL of nitrobenzene for 1 minat 25 ± 0.5�C in an ultrasonic bath (28 kHz, 100 W)
94–99 653–835 GC-FID 0.4–2 lg/L [65]
Water Organochlorinepesticides
LDS-UAEME (6 mL) with 30 lL of isooctane into an 8-mL plastic Pasteur pipette for 30 s at 25 ± 2�C in anultrasonic water bath (35 kHz 0.32 kW).
78–120 128–328 GC-MS 0.8-10 ng/L [66]
Environmental watersamples
Carbamate Pesticide LDS-UAEME (4 mL) with 50 lL of toluene in anultrasonic bath. Comparison with UAEME and LDS-DLLME
88–107 80 On-columnderivatizationGC-MS
0.01-0.1 lg/L [67]
Water 48 Pesticides UAE (10 mL) with 10 mL of acetonitrile by sonication(15 min at 0.5 cycles and 60% amplitude) with anultrasonic probe
75–111 10 LC-MS/MS 0.05-5 ng/mL [68]
Sewage sludge Bisphenol A and itschlorinated derivatives
UAE (1 g into an stainless steel capsule) with 10 mL ofethyl acetate for 20 min at 70% amplitude in anultrasonic bath.Comparison with MAE and PLE
98–103 2 LC–MS/MS 9 ng/g [69]
Sewage sludge Dibutylin and tributylin UAE (0.2 g in a closed tube) with 4 mL of acetic acidfor 30 min in an ultrasonic bathComparison with MAE and mechanical stirring.
– – DerivatizationGC-MSGC-FPDGC-ICP-MS
– [70]
Soil Chlorophenols EME–LDS-UAEME (100 mL) EME under 50 V for10 min, pH of 1; 1-octanol as SLM; 30 lL toluene asLDS-UAEME extraction solvent for 2 min in anultrasonic bath
78–105 2198 Derivatization GC-MS
< 0.005 lg/L [71]
Soil Chlorobenzenes UAE (1 g) with 10 mL of ultrapure water for 30 min at30 �C in an ultrasonic bath (100 W). SBME withhollow fiber membrane that contains about 4 lL of 1-octanol. Comparison with Soxhlet extraction
93–105 250 GC-IT-MS 0.7-27.3 ng/g [29]
Soil Phenylurea herbicides UAE (10 g) with 20 mL of acetonitrile-water (1:1) bysonication (15 min at 0.5 cycles and 60% amplitude)with an ultrasonic probe
76–108 10 LC-MS/MS 0.1- 9.0 ng/g [72]
Biological samples PBDEs UAE (1 g) with 8 mL of n-hexane-dichloromethane(8:2) followed bydSPEC18-silica as sorbent material
75–114 2 GC-MS/MS 9–44 pg/g [73]
Silk worm larvae Sterols UAE (250 mg) using 150 mM NaCl, 50 mM Tris (pH7.5), 2 mM EDTA for 10 min at 4�C in an ultrasonicbath. Then, the Bligh and Dyer method was used.
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established application is to accelerate conventionalextraction methods. UAE, also reported as ultrasound-assisted leaching (USAL), has been widely used to releaseinorganic compounds using acidic and basic solutions[28,30,36,38–40,57]. These procedures do not involvetotal destruction of the sample matrix but the breakdownof the chemical bonds between the trace elements andthe constituents of the sample matrix.
As far as SLE is concerned, the enzymatic hydrolysis ofbiological samples accelerated by ultrasound (known asultrasound-assisted enzymatic extraction, UAEE) is cur-rently the most powerful tool used to extract the totalcontent of inorganic elements whilst maintaining speciesintegrity. It can be used for total elemental determina-tion, elemental speciation and protein characterization[34,35,41]. It is fast (<2 min per extraction), easy tooperate and inexpensive.
UAEE has an important application in the fast moni-toring of peptide/protein biomarkers. In this field, UAE isalso named high-intensity focused ultrasound (HIFU)because only the probe and the cup-horn sonoreactorscan speed the digestion process [34,35]. The ultrasonicbath is inefficient for this purpose. Overall, the ultrasonicapproach can be applied to in-gel separated proteins (1Dor 2D) or proteins dissolved in liquids (including, in thiscase, whole proteomes). It can be used to speed the stepsof denaturation, reduction, alkylation and digestion. Ageneral scheme of this method is shown in Fig. 4. Theapplication of only 1–2 min of HIFU to in-solution trypticdigestions has been reported to achieve efficiency andreproducibility similar to those obtained by traditionalovernight protocols [75].
Ultrasound-assisted solvent extraction is also consid-ered a good option for organic-compound extractionfrom different matrices, as it provides more efficientcontact between solid and solvent due to an increase ofpressure (which favors penetration and transport) andtemperature (which improves solubility and diffusivity).
Figure 4. Sonoreactor approach to enhance in-gel or in-solution protein-idedenaturation, reduction, alkylation and cleaning steps. A volume as low asusually enough to guarantee successful treatment. Temperature generallysonication power of sonoreactors or ultrasonic probes is enough to guaranenzymatic digestions (reproduced with permission from [75]).
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Several extractions can be performed simultaneously,and, as no specialized laboratory equipment is required,the technique is relatively inexpensive compared to mostmodern extraction methods. Several classes of foodcomponents (e.g., aroma, pigments, antioxidants andother organic and mineral compounds), additives andenvironmental contaminants have been extracted andanalyzed efficiently from a variety of matrices (mainlyanimal tissues, food, plant materials, water, soil andsediment) [27,33,53,54]. A wide range of solvents orsolutions can be used and the solvents can be collectedeasily. However, the extraction is still time-consumingand a large volume of organic solvents is required.
Due to its characteristics, UAE can be used as pre-treatment prior to more sophisticated extraction. Forexample, a UAE/solid-phase extraction (SPE)/supercriti-cal fluid extraction (SFE) method was developed for traceconcentrations of isoflavones in algae and cyanobacteria[37]. During the sonication pretreatment, certain partsof the matrix (e.g., walls of the cells or organelles in plantmaterial) are damaged, and the SFE mass transfer takesplace much more easily.
UAE is just a way to assist and to accelerate extrac-tions by coupling with other extraction methods{microwave-assisted extraction (MAE) [56], matrix so-lid-phase dispersion (MSPD) [51] and hollow-fiber liquid-phase microextraction (HF-LPME) [55]}. As an example,Fig. 5 shows the performance of ultrasound HF-LPME(UA-HF-LPME) [55], which improves the separation andthe preconcentration of nicotine from nightshade vegetaland commercial food products.
3.2. Ultrasound-assisted emulsification microextraction(UAEME)More recently, a novel microextraction technique, namedUAEME, or ultrasound-assisted dispersive liquid–liquidmicroextraction (DLLME), was reported by Regueiro et al.[76]. This approach is based on emulsification of a mic-
ntification workflows. The sonoreactor can also be used to accelerate5 lL can be handled in as little as 1 min. 50% sonication amplitude isreached is �50�C, but water can be recirculated or substituted. Thetee acceleration of protein digestion. Ultrasonic baths cannot boost
Figure 5. Operation of ultrasound-assisted hollow-fiber liquid-phase microextraction (UA-HF-LPME) (reproduced with permission from [55]).
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rovolume of water-immiscible extraction solvent in theaqueous sample solution by ultrasound radiation, whichcan increase the contact surface between the twoimmiscible phases, favoring the mass transfer of analytesinto the organic phase and improving the extractionefficiency. More importantly, UAEME does not need thedisperser solvent used in conventional DLLME, whichavoids losses of the target analytes. The main effects ofultrasound are the fragmentation of one of the phases toform an emulsion of sub-micron droplet size that extendsthe contact surface between both liquids.
Combining the benefit of microextraction and ultra-sound radiation has made it possible to establish anefficient preconcentration technique for determininganalytes at trace-concentration levels. In this way,UAEME has been reported for the extraction of foodpreservatives, strobilurin and oxazole fungicides, Sudandyes, polybrominated diphenyl ethers, trichloroanisole,pesticides, and other analytes in liquid samples prior totheir determination by several detection techniques[41,42,44,45,47,48]. The technique is very versatileand, when necessary, UAEME with in situ derivatization(UAEME-ISD) can be performed for simultaneous one-step derivatization, extraction, and preconcentration, asproposed for the determination of bisphenol A in bever-ages using acetic anhydride as the derivatizing agent[45]. There are already many variants reported in theoperation modes of this technique [e.g., injection-ultra-sound-assisted dispersive liquid-liquid microextraction(IUSA-DLLME)]. Here, a small amount (mL) of theextraction solvent is rapidly injected into a large volumeof aqueous sample to form a cloudy solution by a syringewith a home-made porous plastic tip, and then thecloudy solution is immersed immediately into an ultra-sonic water bath for a short time. The performance ofIUSA-DLLME was illustrated by the determination of
copper at the 0.5 ng/mL concentration level in realwater samples by using UV-visible spectrophotometrywith diethyl dithiocarbamate as complexing agent [57].
In the above applications, extraction solvents withdensities higher than water have been most widely usedbecause they can be sedimented by centrifugation andconveniently collected after extraction, although someefforts have been made to apply low-density organicsolvents [66,67]. The simplest reported procedure is touse a plastic Pasteur pipette filled with the sample andthe organic solvent for low-density, solvent-basedUAEME (LDS-UAEME) [66,67]. Fig. 6 shows the proce-dure. Once the pipette had been centrifuged, its bulb wassqueezed slightly, and the upper layer comprising theorganic extract moved into the narrower stem of thepipette. This permitted convenient retrieval of the extractusing a several lL GC microsyringes.
As a more complex example, electro membraneextraction combined with LDS-UAEME (EME–LDS-UAEME) was developed for the determination of chlor-ophenols in water. The method possesses the advantagesof EME and UAEME. Since the membrane in EME pro-tects the acceptor solution from interfering materials, noadditional clean-up was required. Moreover, EME, beingdriven by electrical potential, is much faster than mostconventional microextraction procedures. The analyteswere further preconcentrated by LDS-UAEME. Highextraction efficiency was obtained, due to the combina-tion of the two techniques [71].
Ionic liquid-based UAEME (IL-UAEME) or ultrasound-assisted ionic liquid/ionic liquid dispersive liquid-liquidmicroextraction (UA-IL/IL-DLLME) is based on theemulsification of hydrophobic IL in an aqueous sample byultrasound radiation and further separation of both li-quid phases by centrifugation. In IL-UAEME, ultrasoundand dispersive solvents are utilized to increase the
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Figure 6. Polyethylene Pasteur pipette-based Ultrasound-assisted emulsification microextraction (UAEME) with a low-density organic solvent:(a) introduction of aqueous sample and extraction solvent; (b) ultrasonication for 30 s; (c) phase separation after centrifugation; (d) squeezingthe pipette bulb; and, (e) collection of the extract (reproduced with permission from [66]).
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extraction ability of ILs. The IL-UAEME method has beensuccessfully applied to the pre-concentration of insecti-cides and antibiotics [47,52].
USAEME has also been successfully combined withsolidification of floating organic drop microextraction(SFODME); which uses a water-immiscible solvent hav-ing a melting point in the range 10–30�C [58]. The or-ganic phase with the analytes is easily separated bysolidification. The application of a miniaturized UAE-SFODME approach to determine tellurium using a microvolume of undecanol provides the advantages of bothtechniques.
4. Comparison with other techniques
Several studies reported the comparison of UAE (mainlyin terms of recoveries and duration) with other extrac-tion techniques, either classical or recent.
4.1. Classical techniquesAs the majority of UAE applications deal with solidmatrices, the classical techniques are commonly man-ual shaking, Soxhlet extraction, steam distillation orreflux. Most often, UAE affords several advantages overclassical techniques (e.g., lower solvent consumption,speed, and the potential to recover tightly bound resi-dues not easily released by conventional techniques). Inaddition, UAE is well suited to routine analysis, andsolvents already used for classical methods may bereadily adaptable to UAE.
Shaking and UAE were compared for the extraction ofsodium nifurstyrenate and nitrovin residues from liverusing acetonitrile [27]. The recoveries of both analytesobtained by ultrasonic extraction were better than thoseof than shaking [i.e., 90% and 88% versus 76% and79%, respectively]. Furthermore, ultrasound is easy to
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handle and saves time. Several studies reported similarresults for UAE or Soxhlet extraction in applications{e.g., PBDEs from dust samples [61] or chlorobenzenesfrom soil [29]}.
A comparative study of steam-distillation extraction(SDE), reflux extraction (RE), and UAE was conductedfor the extraction of essential oils from the bud ofCitrus aurantium L. var. amara Engl. Each method wasevaluated in terms of qualitative and quantitativecomposition of the isolated essential oil by gas chro-matography/mass spectrometry (GC-MS). The extractyields of essential oil were 0.2%, 2.2% and 2.3%,respectively; 82 compounds were identified by GC-MS.The main components obtained by SDE were terpinen-4-ol (21.0%), dipentene (11.7%), terpinene (9.2%),those by RE were palmitic acid (20.6%), 2-chloroethyllinoleate (14.5%), tetracosane (12.3%), and a-linolenicacid (11.2%), and those by USE were tetracosane(11.3%), heneicosane (11.1%), and palmitic acid(8.8%). Comparative analysis indicated that SDE wasfavored for extraction of monoterpene hydrocarbons,sesquiterpene hydrocarbons, alcohols, and carbonylcompounds, and RE and USE had certain advantagesin extraction of aliphatic saturated hydrocarbons, or-ganic acids, and esters. It was concluded that differentextraction methods may lead to different yields ofessential oils; the choice of appropriate method is veryimportant to obtain more desired components withhigher physiological activities [53].
4.2. Microwave-assisted extraction (MAE), pressurized-liquid extraction (PLE) and supercritical-fluidextraction (SFE)Among the more recently developed solvent extractiontechniques, MAE and pressurized liquid extraction (PLE)showed the highest extraction yields in food processing,with short extraction times and easy operation, due to
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the high degree of automation [1,3]. In comparison, UAEoffered a simpler extraction procedure, requiringamounts of solvent similar to MAE and PLE, but longeranalysis times [1,3].
Despite the differences in the extraction procedures,the three methods exhibited similar analytical parame-ters in relation to sensitivity, selectivity, accuracy andprecision. The three techniques were compared in orderto evaluate their efficiency in the extraction of bisphenolA and its chlorinated derivatives with ethyl acetate fromsewage-sludge samples. The results showed no statisti-cally significant differences between the three extractiontechniques for the determination of BPA. Selection of atechnique is determined by price-related rather thananalytical factors. One of the most important contribu-tions of this work is the demonstration that the threeevaluated extraction techniques are all useful, offeringaccurate and precise determination of compounds [69].
PBDEs were extracted from dust samples, applying threedifferent extraction techniques (i.e. Soxhlet extraction, PLEand UAE) and different organic solvents [61]. Good resultsfor all studied congeners were observed for PLE, applyingboth n-hexane and dichloromethane-n-hexane (1:1) asextraction solvents. High recoveries were also reported forSoxhlet extraction (dichloromethane, dichloromethane-hexane (1:1)) and UAE (toluene). Finally, while UAE givesextraction efficiencies comparable to MAE and PLE, withsimilar extraction times, MAE and PLE require greaterinvestment (for more expensive equipment).
Among different extraction procedures (includingUAE), SFE showed the highest extraction yields for 39fatty extracted from pulverized Microulasikkimensis seed[54]. The entire extraction process was almost completedwithin 90 min and the extraction yield of SFE could at-tain 34.0%. The three other extraction methods tested[microwave-assisted reflux extraction (MWRE), USE andRE] were carried out with dichloromethane and theextraction yields for them were: MWRE, 13%; USE, 7%;and, RE, 12%. Furthermore, SFE is more efficient andcompatible for extraction of chemicals from naturalmedicines or foods than MWRE, UAE and RE because ituses no organic solvents [54].
4.3. Liquid-liquid microextraction (LLME)The performance of UAE have also been compared torecent liquid-liquid microextraction (LLME) techniquesdedicated to the treatment of solid and liquid samples:drop-to-drop solvent microextraction (DDSME), single-drop microextraction (SDME), ionic liquid-homogeneousliquid-liquid microextraction (IL-H-LLME) and ionic li-quid-temperature-controlled-dispersive liquid-liquidmicroextraction (IL-TC-DLLME). Although these tech-niques are relatively new, there are already a number ofstudies that compare their performances to UAE.
The potential of UA-HF-LPME was compared with thatof DDSME by calculating the enrichment factors (EF) and
limits of detection (LODs) at the optimized conditions forspiked tomatoes. The EFs obtained for UA-HF-LPME andDDSME were 19 and 5, respectively. A four-foldimprovement in the EF and LODs also showed that UA-HF-LPME was better for separation and preconcentrationof nicotine from nightshade vegetal samples [55].
As an illustration of the efficiency of UAEME, therecoveries of several strobilurin and oxazole fungicideswere compared with those obtained by SDME [48]. Theuse of low-density organic solvents appeared appropriatefor both miniaturized procedures. Comparison of theequilibrium time and extraction temperature indicatedthat UAEME is advantageous for extraction of fungicides,as equilibrium was reached in a few seconds at roomtemperature, meaning it is a more precise, robustmethod. EFs were 140–1140 for the target fungicidesusing UAEME and 80–1600 using SDME. The extractionrecoveries were similar for both methods (80–119%).LODs were 6–75 ng/L and 100–310 ng/L for UAEMEand SDME, respectively.
The performances of UA-IL/IL-DLLME, IL-H-LLME, IL-UAEME and IL-TC-DLLME were compared for the deter-mination of sulfonamides in infant formula milk powder.Slightly higher recoveries (90–115) were observed withUA-IL/IL-DLLME, especially for sulfamethoxazole. Also,both UAE methods performed better than traditionalLLME [47].
The extraction efficiencies of Cu(II) by (1) LLE, (2)injection-assisted DLLME, (3) ultrasound-assisted DLLMEand (4) IUSA-DLLME were compared by measuring theabsorbance at the maximum absorption wavelength(435 nm) of the Cu–diethyl-dithiocarbamate complex[57]. In comparison with LLE, the three DLLME proce-dures gave improved absorbance; IUSA-DLLME gave thehighest absorbance (i.e. about twice the absorbance ofLLE). Ultrasound-assisted DLLME gave lower absorbancethan IUSA-DLLME for concentrations above 12.5 ng/mLof copper, because, in a given time, the speed and thedegree of dispersion of ultrasound-assisted DLLME arelower than those of IUSA-DLLME. It was observed that,at the start of the dispersion process of ultrasound-as-sisted DLLM, only part of the organic solvent dispersedinto the aqueous phase, the other part remaining as aseparate phase at the bottom of the tube, with the‘‘cloud’’ developing gradually from the bottom to theupper part of the tube.
LDS-UAEME, conventional UAEME and low-densitysolvent-based DLLME (LDS-DLLME) were also comparedfor the extraction of carbamate pesticides from environ-mental water samples [67]. LDS-UAEME had someadvantages. Most importantly, no dispersive solvent isneeded in LDS-UAEME. In DLLME, this usually amounts tohundreds of lL. This is the most prominent advantage ofUAEME over DLLME. Furthermore, the toluene employedin LDS-UAEME in the present work was much less toxicthan chlorinated solvents widely used in conventional
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UAEME. The proposed method offers a simple, practicalapproach to extend the range of suitable solvents forUAEME use, overcoming the limitation of high-densitychlorinated extraction solvents necessary for conven-tional DLLME with centrifugation in order to collect thefinal extract at the bottom of the extraction vessel.
5. Final remarks
Even though the use of ultrasound energy to enhancethe extraction of organic compounds is rather recent,numerous applications have extracted compounds infood and environmental matrices. Several classes ofcompounds (e.g., PAHs, pesticides, inorganic com-pounds, antibacterials, preservatives, dyes, trichloroani-soles, essential oils, fatty acids, isoflavones and peptides)have been extracted efficiently from a variety of matrices(mainly soils, sediments, animal tissues, and vegetables),either spiked or containing incurred compounds. All thereported applications show that UAE is a viable alter-native to conventional techniques for such matrices.Comparable efficiencies have been reported along withacceptable reproducibilities. In addition, UAE offers agreat reduction in time and solvent consumption, as wellas the opportunity to perform multiple extractions. Evi-dence has also been presented that UAE may competefavorably with recent techniques (e.g., MAE, PLE andLLME). In particular, optimization of UAE conditions israther easy, due to the small number of parameters (i.e.matrix moisture, nature of solvent, and time) comparedto the other techniques.
Finally, it appears that use of UAE in analytical labo-ratories should increase in the next few years, especiallydue to the reasonable cost of the equipment.
AcknowledgmentsThis work has been supported by the Spanish Ministry ofEconomy and Competitiveness through the project‘‘Assessing and predicting effects on water quantity andquality in Iberian rivers caused by global change’’(SCARCE) Consolider-Ingenio 2010 (CSD2009-00065)and ‘‘Evaluation of Emerging Contaminants in the TuriaRiver Basin: from basic research to environmentalforensics applications’’ (CGL2011-29703-C02-02).
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