DLLMe

Journal of Chromatography A, 1335 (2014) 214

Contents lists available at ScienceDirect

Journal of Chromatography A

jo ur nal ho me pag e: www.elsev ier .com/ locate /chroma

Review

Beyond dispersive liquidliquid microextraction

Mei-I. Lea Centro de Segb Department oc Department o

a r t i c l

Article history:Received 24 OReceived in reAccepted 10 FAvailable onlin

Keywords:Dispersive liquDispersion liquid-phase microextractionPreconcentrationSample preparation

tion, DLLME methods are separated in two categories: DLLME with low-density extraction solvent andDLLME with high-density extraction solvent. Besides these methods, many novel special devices for col-lecting low-density extraction solvent are also mentioned. In addition, various dispersion techniqueswith LPME, including manual shaking, air-assisted LPME (aspirating and injecting the extraction mix-ture by syringe), ultrasound-assisted emulsication, vortex-assisted emulsication, surfactant-assistedemulsication, and microwave-assisted emulsication are described. Besides the above methods, com-

Contents

1. Introd1.1.

1.2.

2. Devel2.1.

CorresponE-mail add

1 Tel.: +886

http://dx.doi.o0021-9673/ binations of DLLME with other extraction techniques (solid-phase extraction, stir bar sorptive extraction,molecularly imprinted matrix solid-phase dispersion and supercritical uid extraction) are introduced.The combination of nanotechnique with DLLME is also introduced. Furthermore, this review illustratesthe application of DLLME or dispersion LPME methods to separate and preconcentrate various organicanalytes, inorganic analytes, and samples.

2014 Elsevier B.V. All rights reserved.

uction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3DLLME with lower-density extraction solvent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.1.1. DLLME based on solidication of oating organic droplet (DLLME-SFO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.1.2. DLLME with special extraction devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.1.3. Low-density-solvent based solvent demulsication DLLME (LDS-SD-DLLME). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7DLLME with higher-density extraction solvent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.2.1. DLLME with low-toxicity solvent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.2.2. Auxiliary solvent to adjust the density of DLLME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.2.3. DLLME with automated online sequential injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

opment of DLLME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Various techniques for assisting dispersion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.1.1. Manual shaking for assisting dispersion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.1.2. Air-assisted liquidliquid microextraction (AALLME) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.1.3. Ultrasound-assisted emulsication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

ding author. Tel.: +886 3 572 1194; fax: +886 3 573 6979.resses: [email protected] (M.-R. Fuh), [email protected] (S.-D. Huang).2 2881 9471x6821; fax: +886 2 2881 1053.

rg/10.1016/j.chroma.2014.02.0212014 Elsevier B.V. All rights reserved.onga, Ming-Ren Fuhb,1, Shang-Da Huangc,

uranca Alimentar, Instituto para os Assuntos Cvicos e Municipais (IACM), Macau, Chinaf Chemistry, Soochow University, Taipei 11102, Taiwanf Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan

e i n f o

ctober 2013vised form 9 February 2014ebruary 2014e 15 February 2014

idliquid microextraction

a b s t r a c t

Dispersive liquidliquid microextraction (DLLME) and other dispersion liquid-phase microextraction(LPME) methods have been developed since the rst DLLME method was reported in 2006. DLLMEis simple, rapid, and affords high enrichment factor, this is due to the large contact surface area ofthe extraction solvent. DLLME is a method suitable for the extraction in many different water sam-ples, but it requires using chlorinated solvents. In recent years, interest in DLLME or dispersion LPMEhas been focused on the use of low-toxicity solvents and more conveniently practical procedures. Thisreview examines some of the most interesting developments in the past few years. In the rst sec-

M.-I. Leong et al. / J. Chromatogr. A 1335 (2014) 214 3

2.1.4. Surfactant-assisted emulsication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.1.5. Vortex-assisted emulsication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.1.6. Microwave-assisted emulsication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.2. Combination of techniques for extraction and analysis with DLLME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10. . . . . .

with. . . . . . . . . . . .

2.3. . . . . . . 3. DLLM . . . . . .

3.1. . . . . . . . . . . . .. . . . . .

3.2. . . . . . .4. Concl . . . . . .

Con . . . . . .Ackno . . . . . .Refer . . . . . .

1. Introdu

Liquidlextraction ooperationalporous holvent. The organic solsurface aretion times. Imicroextracmatic hydromethods emwater-misction solvendisperser sohigher thanin both wat5 mL of the with a conicvent) and 8is injected ing of watethe test tubextraction pcould be inMany convesolvents as510 mL of centrifugatinique incluenrichmenttion solventcarbon tetra

There arsion LPME mextraction) DLLME usincludes the (based on socedures, theproceduresanalysis [9]applicationceuticals, ot

e nepmeries: aterater d seviallyhich

adfar DLLMconc

andarizesion dever betn of

for Dds inendi

to o extion een om siliarymeths so2.2.1. Solid-phase extraction combined with DLLME . . . . . . . . . . . . . . . . . . 2.2.2. Stir bar sorptive extraction (SBSE) combined with DLLME . . . . . . 2.2.3. Molecularly imprinted matrix solid-phase dispersion combined2.2.4. Supercritical uid extraction (SFE) combined with DLLME . . . . . 2.2.5. Nanotechniques combined with DLLME . . . . . . . . . . . . . . . . . . . . . . . . . Other methods using low-toxicity solvent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

E applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Application of DLLME for various analytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.1. Organic compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.2. Inorganic compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Application of DLLME to various eld samples . . . . . . . . . . . . . . . . . . . . . . . . . . . .

usion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ict of interest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . wledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ction

iquid microextraction (LPME) is usually applied in thef environmental samples. LPME has several different

modes, such as those that use a drop of solvent [1,2],low ber-protected solvent [35], and disperser sol-rst two methods are simple and use lower volumes ofvent. However, they are limited by the small contacta of the drop or ber, which necessitates long extrac-n 2006, Rezaee et al. developed dispersive liquidliquidtion (DLLME) for preconcentration of polycyclic aro-carbons (PAHs) in water samples [6]. The rst DLLMEploy a mixture of a high-density extraction solvent, a

ible solvent, and a polar disperser solvent. The extrac-t must be able to extract analytes, is soluble in thelvent, insoluble in aqueous samples, and have density

that of water. The disperser solvent has to be solubleer and extraction solvent. In this method (Fig. 1(a)) [6],aqueous solution is placed in a screw-cap glass test tubeal bottom. A solution of 1 mL of acetone (disperser sol-

L of tetrachloroethylene (TCE, the extraction solvent)into the sample solution. A cloudy dispersion consist-r, disperser solvent, and extraction solvent is formed ine and is centrifuged. The dispersed ne droplets of thehase settle at the bottom of the conical test tube andjected into a gas chromatograph for further analysis.ntional DLLME typically use 20100 L of chlorinated

extraction solvent, 0.52 mL of disperser solvent, and

of thesdevelocategothan wthan wmarizebe initvent, w[12]. Dtion offor premetalssummdispervents, transfebinatiodevicemetho

Depbelongdensityextracthave bvent fran auxthese sampleaqueous sample. The total extraction time including theon time is generally 510 min. Advantages of this tech-de simplicity of operation, rapid extraction, and high

factors (EFs) [7,8]. However, the high-density extrac- used, which is typically chlorobenzene, chloroform, orchloride, is highly toxic.e many excellent recent reviews on DLLME or disper-ethods (methods that disperse extraction solvent for

[913]. Kocrov et al. summarized a lot of details aboutg organic solvents lighter than water methods, and con-uses of special devices, the low-density solvent usedlidication and solvent demulsication) in DLLME pro-

adjustment of extraction solvents mixture density and based on automation of DLLME by sequential injection. Zgoa-Grzeskowiak and Grzeskowiak described the

of DLLME to pre-concentration of metal ions, pharma-her organic compounds and many more modications

mated procanalytical m

1.1. DLLME

1.1.1. DLLM(DLLME-SFO

Liquidlorganic dro[14,15]. It istion of orgathat of DLLMbenets of does not inDLLME, it dglass tubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 DLLME (MIMMSPDDLLME) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

wly developed techniques [10]. Kokosa reviewed thent of DLLME and summarized the techniques in threeDLLME using extraction solvents with density greater, DLLME using extraction solvents with density lowerand automated DLLME [11]. Asensio-Ramos et al. sum-eral DLLME applications in food analysis. Analytes can

extracted from the food matrix with an organic sol- normally acts in a second step as the disperser solventnia and Shabani summarized and discussed the applica-E in combination with different analytical techniques

entration and determination of ultra trace amounts of organometal ions in various matrices [13]. This reviewd and discussed the recent developments of DLLME andLPME including the utilization of various less toxic sol-lopment various techniques to increase rate of massween two extracting solvent and sample solution, com-

other extraction with DLLME and design of specialLLME. Abbreviations of the DLLME and dispersion LPME

this review are shown in Table 1.ng on the extraction solvent used, DLLME method mayne of two broad categories: those that use a lower-raction solvent and those that use a higher-densitysolvent. Many new techniques in the former categoryintroduced to separate and collect the extraction sol-ample solution. Brominated or iodinated solvents and

solvent in the latter category have been introduced;ods enable easy separation of extraction solvent andlution by centrifugation. Other novel online and auto-

edures with DLLME that have a promising future inethodology are also mentioned in this section.

with lower-density extraction solvent

E based on solidication of oating organic droplet)iquid microextraction based on solidication of oatingplet (LLME-SFO) was introduced by Khalili-Zanjani et al.

simple, inexpensive, and it involves minimal consump-nic solvent. However, its extraction rate is lower thanE. DLLME-SFO [16,17] was developed to combine the

DLLME and LLME-SFO. Unlike LLME-SFO, DLLME-SFOvolve stirring during extraction, and unlike traditionaloes not use chlorinated solvents and conical bottom. Instead, a mixture of low-toxicity extraction solvent

4 M.-I. Leong et al. / J. Chromatogr. A 1335 (2014) 214

Fig. 1. Diagram of the extraction process of (a) DLLME and (b) DLLME-SFO.

Table 1The abbreviations of the DLLME and dispersion LPME methods in this review.

Method Abbreviation of the method Ref.

Dispersive liquidliquid microextraction DLLME [6]

DLLME with lower density extraction solventDLLME based on the solidication of a oating organic drop DLLME-SFO [16,17]Ionic liquid-based up-and-down shaker-assisted DLLME UDSA-IL-DLLME [25]Low-density solvent-based solvent demulsication DLLME LDS-SD-DLLME [26]

DLLME with higher density extraction solventLow toxic DLLME LT-DLLME [28]Adjust the density of DLLME AS-DLLME [29]Injection dispersive liquidliquid microextraction SI-DLLME [3033]

Various techniques for assisting dispersionDLLME with a very low solvent consumption DLLMELSC [34]Air-assisted liquidliquid microextraction AALLME [35]Ultrasound-assisted emulsication microextraction USAEME [3645]Surfactant assisted DLLME SA-DLLME [22,23]Coacervative microextraction ultrasound-assisted back-extraction technique CME-UABE [39]Water with low concentration of surfactant in dispersed solvent-assisted emulsion dispersive

liquidliquid microextractionWLSEME [46]

Low-density solvent-based vortex-assisted surfactant-enhanced-emulsication liquidliquidmicroextraction

LDSVSLLME [48]

Vortex-assisted supramolecular solvent microextraction VASUSME [49]Vortex-assisted liquidliquid microextraction VALLME [38,4749]Homogeneous ionic liquid microextraction HILME [50]

Combination of techniques for extraction and analysis with DLLMESolid-phase extraction combined with DLLME SPE + DLLME [51]Stir bar sorptive extraction combined with DLLME SBSE + DLLME [52]Matrix solid-phase dispersion combining with DLLME MSPDDLLME [53]Supercritical uid extraction followed by DLLME SFE + DLLME [54,55]Dispersive microsolid-phase extraction combined with DLLME D--SPE + DLLME [56,57]Vortex-assisted micro-solid-phase extraction followed by low-density solvent based DLLME VA--SPE + LDS-DLLME [58]

Other methods using low-toxicity solventFlotation-assisted homogeneous liquidliquid microextraction FA-HLLME [76]


(which is also less dense than water) and disperser solvent arerapidly injected into the sample solution to form a cloudy disper-sion in the glass test tube. In this method [16] (Fig. 1(b)), a mixtureof 0.5 mL of acetone and 10 L of 2-dodecanol is rapidly injected bysyringe intois transferred solventabout the cposal, this mlow volatiliand the droextraction tLLME-SFO [the solventwarm clima

1.1.2. DLLMRecently

toxicity solOne possibDLLME is thdesigned ceFarajzadeh to extract oextraction mand acetonean aqueousdroplets of solution. Thseparation. tant; howevHashemi etdevice to en(Fig. 2(b)) [(NNGT) insused as theA uniformlyaspiration asyringe. Thehexanol is lthe surface the openingthe narrow be withdraw

Saleh etfor ultrasou(Fig. 2(c)) fothis methodaqueous sabath. After a gas chromextraction athis and thedifculty ofdesigned a sof which hain environmto facilitateis used as tvent is usedAfter extraseparation easily achieeral minuteconcentratepure water

is thereafter withdrawn by microsyringe for HPLC analysis. Thismethod is faster than many DLLME methods because it does notrequire centrifugation. It can be applied in the extraction of samplesthat are non-volatile and have large volumes. Hu et al. developed

DLLMr comethodlytenstectly alyte

the injeette

mixes so

easils thend e

Jen om w

ion [2 emut in xtra

into syrine need intltras

is sated

get Oted e5 mL00

recoractahis mractasave

asstrate-dowactioted iThe phonol (2shak

micralysparathang proy suct norpersile 2. s canom to gatant, o reamether th a 5 mL water sample. After centrifugation, the test tubeed to a beaker containing crushed ice, and the solidi-

is easily collected for analysis. To meet recent concernsosts and environmental hazards of waste solvent dis-ethod uses an extraction solvent of low toxicity and

ty. The large contact surface area between the sampleplets of extractants facilitate mass transfer, resulting inimes similar to those of DLLME and shorter than that of14,15,18]. The drawbacks of this method are limited to

chosen (low melting point) which is suitable for use intes, if the laboratory is not air conditioned.

E with special extraction devices, many researchers have attempted to use lower-vents with density lower than that of water in DLLME.le way of enabling the application of such solvents ine use of special extraction devices, such as speciallyntrifugation tubes and pipette collection tubes. In 2009,et al. designed a special vessel [19] for use in DLLMErganophosphorus pesticides (OPPs) (Fig. 2(a)). In thisethod, a mixture of cyclohexane (extraction solvent)

(disperser solvent) is rapidly injected by syringe into sample in a special vessel. After centrifugation, necyclohexane accumulate in the upper layer of aqueouse upper phase is injected into a gas chromatograph forThis method is rapid and easily recovers the extrac-er, it is not suitable for extracting volatile compounds.

al. developed a DLLME method that uses a specialrich glycyrrhizic acid from aqueous extracts of licorice20]. The device consists of a narrow-necked glass tubeerted into a centrifuge tube. Hexanol and acetone are

extraction solvent and disperser solvent, respectively. distributed cloudy suspension is produced by furthernd expulsion of about 2 mL of the cloudy sample by

mixture is then centrifuged for phase separation. Sinceighter than water, the extraction phase accumulates onof the aqueous solution. Additional water is added from

of NNGT; then, the extraction phase is raised and llsneck of NNGT. As a result, the extraction phase can easilyn by microsyringe.

al. reported a centrifuge glass vial fabricated in-housend-assisted emulsication microextraction (USAEME)r the determination of PAHs in water samples [21]. In, the extraction solvent toluene is injected slowly into

mple in a centrifuge glass vial in an ultrasonic watercentrifugation, the separated toluene is injected intoatograph for analysis. This method affords very rapidnd recovery of the extractant. The only drawback of

aforementioned method by Hashemi et al. [20] is the cleaning the centrifuge glass vial. In 2011, Zhang et al.pecial ask equipped with two narrow open ports, ones a capillary tip [22] to extract ultraviolet (UV) ltersental water samples (Fig. 2(d)). The ask is employed

the DLLME process. 1-Octanol, a low-density solvent,he extraction solvent for DLLME and no disperser sol-. The extraction is accelerated by magnetic agitation.

ction, no centrifugation step is necessary, and phaseof the extraction solvent from the aqueous sample isved by allowing the extraction mixture to stand sev-s. The organic phase rises to the top of the mixture ands in the narrow open tip of the ask upon addition of

into the extraction mixture through the other port. It

[23] a of polathis mthe ana(TBP) iis direthe anture ofrapidlythe pipvortexaqueouand is expandlytes, aSu andOPPs frdetectate thesolvenmicroedrawnof the and thinjecteAfter usyringea graduthe tarseparauses a and a 1and tothe exttube. Tthe ext

To shakerconcenup-andof extrfabricatubes. auoromethadown then ather anThe apis less shakintoxicitsolven

Disin Tabdevicevent frports textractdrop tOther to gathE method based on a molecular complex for analysispounds in aqueous solution (Fig. 2(e)). The principle of

is the hydrogen bonding between the extractant ands. In this approach, the Lewis base tri-n-butylphosphatead of conventional water-immiscible organic solventsused as extractant for DLLME. The sample containings is placed in a disposable polyethylene pipette. A mix-extractant TBP and the disperser solvent methanol iscted into the sample solution by syringe. Subsequently,is placed in a 10 mL Eppendorf tube and is agitated by ar. After centrifugation, the organic phase oating on the

lution is concentrated in the narrow neck of the pipette,y withdrawn by a 10.0 L microsyringe. This technique

application of classical DLLME for various organic ana-nables extraction in a disposable polyethylene pipette.developed an in-syringe USAEME for the extraction ofater samples by using GC with micro electron capture4] (Fig. 2(f)). Ultrasound radiation is applied to acceler-lsication of microliter volumes of low-density organicaqueous solutions to enhance the efciency of OPPsction from the sample. Initially, the sample solution isa 5 mL syringe. After removal of the plunger and sealingge with a silicone-plug, the barrel is held upside downdle is removed. The extraction solvent (toluene) is theno the sample solution by using a 100 L glass syringe.onication and centrifugation, the plunger of the 5 mLlowly pushed to transfer the recovered extractant into

capillary tube. Finally, the extracting phase containingPPs is easily recovered by syringe. One microliter of thextractant is injected into GC for analysis. This method

syringe as the sample vial instead of a centrifuge tube,L glass syringe is used to inject the extraction solventver the extractant. This device is easy to operate, andnt volume is easily read from the scale on the capillaryethod does not require a narrow-necked port to collectnts and the device is very easy to clean.time and effort, Ku et al. performed an up-and-downisted DLLME that uses an ionic liquid (IL) to pre-

three UV lters from eld water samples [25]. Then shaker model FS-6 was used to shake the mixture

n solvent and aqueous sample. In this method, a holdern-house is used to hold the sealed conical-bottom glassextraction solvent 1-octyl-3-methylimidazolium hex-sphate ([C8MIM][PF6]) (40 L) and the disperser solvent00 L) are used to extract the UV lters. After up-and-

ing for 3 min, the aqueous mixture is centrifuged, andotube is used to collect the extraction solvent for fur-is by ultra-performance liquid chromatography (UPLC).tus for this method is simple and the extraction time

4 min. This method also addresses the variation of thecess due to different operators. In addition, an IL of lowh as [C8MIM][PF6] is used instead of the highly toxicmally used in DLLME.ons in various special extraction devices are describedThe use of the narrow parts (neck, port, or nozzle) of

assist the collection of the low-density extraction sol-he samples. Most of the devices use narrow necks orher the extractant drops [1922]. Before removal of thewater must be injected to allow the extracted organicch the level of the neck or port of the tube or ask.ods that use the nozzle of a pipette [23] or syringe [24]e extractant do not require injection of water and the


Fig. 2. Diagram of the special device used in dispersion LPME with low-density extraction solvent: (a) special extraction vessel (DLLME), (b) glass tube with narrow neck(DLLME), (c) centrifuge glass vial designed in-house (USAEME), (d) special ask equipped with two narrow open ports (DLLME), (e) 5 mL polyethylene Pasteur pipette (DLLME),(f) 5 mL syringe as sample vial (DLLME) and (g) disposable polyethylene pipette (LDS-SD-DLLME).


Table 2Dispersion in different special extraction devices.

Fig. 2 Special sample vessel/tube/vial Method Instrumentation Analytes Extraction solvent Ref.

(a) A special extraction vessel DLLME GC-FID OPPs Cyclohexane [19](b) A LC (c) A -FID (d) A LC (e) A -EC(f) A LC (g) A MS

extraction ause a specidown shakeextraction mdispersion o

1.1.3. Low-(LDS-SD-DL

All of thtages and dcomplexityfor the deteples (Fig. 2A 5 mL sampipette by un-hexane (5injected rapan emulsioninjected intseparate it iis collectedetry (GCMis thereforeThis methoused as extrto a wider r

Chang ecollection scollected exumes of lowmethanol) twater samporganic drowall of the along with syringe. Tharate in thesyringe andover, it is befor about 1 in this manvent collectthe injected

1.2. DLLME

1.2.1. DLLMIn addit

developed using higheovercome twas develotoxicity brosuch as 1the median

toxistrat

as 5wated theidlye is s, 40%ion bugatical t intoion s. In pnven

Auxilrov) tec, an t is e

solv of ts seetho

solu tubetract

tetra glass

of ses at

andthe e

absoagest and

DLLMhemtial

syste ofs mix. Aftcrocis by glass tube with a narrow neck DLLME HP home-designed centrifuge glass vial USAEME GC special ask equipped with two narrow open ports DLLME HP 5-mL soft polyethylene Pasteur pipette DLLME GC 5 mL syringe as the sample vial DLLME HP disposable polyethylene pipette LDS-SD-DLLME GC

pparatus is easy to clean. Except for the methods thatal ask [22] for magnetic agitation or use an up-and-r [25] to disperse the extraction solvent, there are manyethods use disperser solvent or surfactant to assist thef the extraction solvent.

density-solvent based solvent demulsication DLLMELME)e aforementioned extraction devices possess advan-rawbacks in terms of ease of operation and manifold. Guo and Lee [26] reported a LDS-SD-DLLME methodrmination of 16 priority PAHs in environmental sam-(g)). No centrifugation is required in this procedure.ple solution is placed in a 5 mL polyethylene Pasteursing a 5 mL syringe. A mixture of the extraction solvent0 L) and the dispersive solvent acetone (500 L) isidly into the sample solution by a 1.0 mL syringe to form. The demulsication solvent acetone (500 L) is theno the aqueous solution to break up the emulsion andnto two layers. The upper layer (about 35 L n-hexane)

and analyzed by gas chromatographymass spectrom-S). Notably, the extraction requires only 23 min, and

faster than conventional DLLME or similar techniques.d permits a solvent that is less dense than water to beaction solvent, and expands the applicability of DLLMEange of solvents.t al. used DLLME combined with an improved solventystem to separate water and organic solvent in thetractant drop [27]. This method uses very small vol--toxicity solvents (11 L of 1-nonanol and 400 L of

o extract organochlorine pesticides (OCPs) from 10 mLles prior to analysis by GC. After centrifugation, a liquidp accumulates between the water surface and the glasscentrifuge tube. The liquid organic drop is transferredsome of the water into a microtube (3 mm 15 mm) bye organic and aqueous phases then immediately sep-

microtube. The organic solvent is easily collected by then injected into the GC instrument for analysis. More-tter to centrifuge the collected phases in the microtubemin before injection, because it further removes water;ner, two clear phases are obtained. This improved sol-ion system can protect the instrument from damage by

water and increase the reproducibility of the results.

with higher-density extraction solvent

E with low-toxicity solvention to the many DLLME methods that have been

highlydemonas littleple of acid anare rapmixtur(88 Lformatcentrifthe coninject iextractDLLMEthe coLPME.

1.2.2. Koc

DLLMEsamplesolvenrinateddensityitate itThis msampletrifugethe excarbon0.5 mLA layermulatesyringetively, atomicadvantsolven

1.2.3. Ant

sequenDLLMEmixturagent isystemin a mianalysto use low-density organic solvents, other methodsr-density extraction solvent have been introduced tohe drawbacks of normal DLLME. In 2010, LT-DLLMEped by Leong et al. [28]. This method uses lower-minated, iodinated and other halogenated solvents-bromo-3-methylbutane (1-bromo-3-methylbutane,

lethal dose (LD50) 6150 mg kg1) instead of the

[30,31], or absorption does not redenser thanthis methodand severallytes. AndruGlycyrrhizic acid n-Hexanol [20]PAHs Toluene [21]UV lters 1-Octanol [22]

D OPPs Toluene [23]Phenols TBP [24]PAHs n-Hexane [26]

c solvents normally used in DLLME. This method alsoes that propionic acid is suitable as a disperser solvent;0 L of the acid is sufcient for extraction. A 7 mL sam-r is spiked with PAHs. The disperser solvent propionic

extraction solvent 1-bromo-3-methylbutane (10.0 L) injected into the sample solution and the resultinghaken by hand for a few seconds. Potassium hydroxide

(w/v)) is added to the sample to minimize emulsiony the extraction solvent before centrifugation. After

ion, the organic solvent is sedimented at the bottom oftest tube, and then a microsyringe is used to collect and

a gas chromatograph for further analysis. The selectedolvent is less toxic than chlorinated solvents in normalarticular, some brominated solvents are less toxic thantional low-density solvents in DLLME or dispersion

iary solvent to adjust the density of DLLME et al. [29] developed an adjusting-density DLLME (AS-hnique. A quaternary system consisting of an aqueousextraction solvent, an auxiliary solvent, and a dispersermployed in this method. The auxiliary solvent (a chlo-ent), which is denser than water, is used to adjust the

he extraction solventauxiliary solvent mixture to facil-paration from the aqueous sample by centrifugation.d does not require the use of special devices. A 5 mLtion containing Au (III) is prepared in conical microcen-s. A 0.5 mL mixture of the disperser solvent methanol,

ion solvent toluene (145 L), and the auxiliary solventchloride (CCl4; 145 L) is vigorously injected by using a

syringe. The mixture is gently shaken and centrifuged.diment containing a mixture of toluene and CCl4 accu-the bottom of the tube. The extractant is removed by

then analyzed by UVvisible spectrometer. Alterna-xtractant may be transferred to a graphite atomizer forrption spectroscopy. This novel method combines the

of conventional DLLME and the use of lower-density lower volumes of toxic solvents.

E with automated online sequential injectionidis and Ioannou developed an automated on-lineinjection dispersive liquidliquid microextraction SI-em for metal preconcentration [3032] (Fig. 3(a)). The

disperser solvent, extraction solvent, and chelatinged with a stream of aqueous sample through an online

er extraction, droplets of the organic phase are retainedolumn. The eluent is then transferred by a nebulizer for

ame atomic absorption spectrometry (FAAS) analysis

injected into a graphite tube for electrothermal atomicspectrometry (ETAAS) measurement [32]. This methodquire centrifugation and an extraction solvent that is

water, and the process is fully automated. However, requires a microcolumn for retention of the analytes

hundred microliters of solvents for elution of the ana-ch et al. [33] reported a novel SI-DLLME (Fig. 3(b)). In


Fig. 3. Diagramconical tube.

the methodcoil of the resulting mthe extracticloudy suspconsequentAfterward, Z-ow cell methods acthe difculorganic solv

2. Develop

Recent ttoxic solvenaqueous samextraction t

2.1. Variou

2.1.1. ManuTsai and

solvent (DLume of orgaaqueous sato a glass c(300 mg) is13 L mixt

solvent diethyl ether at a ratio of 6:4 is added to the tube, andthen the tube is shaken vigorously for 90 s. Fine organic dropletsare subsequently formed in the sample solution by manuallyshaking the test tube containing the mixture of sample solution

tractts incextraethoantitsion a

Air-aajzadtion mplets ars saes ined

by Gt andersede instanic unds

Ultraasou] reda et aund

by icibleand exdropleto the This mand qudisper

2.1.2. Far

extracous sadropleaqueoueral timperformminedsolvenis dispsyringtle orgcompo

2.1.3. Ultr

[24,38FontanUltrasociencyimmis of (a) SI-DLLME with retention microcolumn and (b) SI-DLLME with

, sample and all reagents are drawn into the holdingsequential injection analysis (SIA) manifold, and theixture is delivered into a conical tube. A mixture ofon solvent is then added at a high ow rate to form aension and to extract the analytes. The extraction phasely separates rapidly at the bottom of the conical tube.the extraction phase is transferred to a microvolumefor spectrophotometric detection. The online DLLMEhieved a major breakthrough in DLLME and overcameties of rapidly extracting analytes and collecting theent in online analysis.

ment of DLLME

rends in DLLME include the use of lower volumes of lessts and techniques for dispersing extraction solvents andples rapidly. Table 3 shows the extraction solvents and

imes for various techniques.

s techniques for assisting dispersion

al shaking for assisting dispersion Huang reported DLLME with very low consumption ofLMELSC) method [34]. In DLLME-LSC, much less vol-nic solvent is used as compared with DLLME. A 10 mLmple spiked with each targeted OCP is transferredentrifuge tube with conical bottom. Sodium chloride

added to the glass tube and dissolved completely. Aure of the extraction solvent TCE and the disperser

method basmusk fragraplaced in a the surrogaple. A 100 chloroforman ultrasonpower for 1rupted by cthe bottomsyringe andinsert in a 1by GCMS.sive alternaextraction (similar appsound and sthe low con

Howeveperiods maindicated tthe extractiwhich minused ultrassuspensionUSAEME mLees group

2.1.4. SurfaSurfacta

HPLC has bof chlorophthis approaion solvent. The large surface area of the organic solventreases the rate of mass transfer from the water samplectant, and allows efcient extraction in a short period.d is a rapid and convenient procedure for qualitativeative analyses of OCPs. Manual shaking may be done fornd extraction, or as a premixing step before extraction.

ssisted liquidliquid microextraction (AALLME)eh and Mogaddam developed an AALLME method forand preconcentration of phthalate esters from aque-s prior to GC analysis [35]. In this method, ne organice formed by aspirating and expelling the mixture ofmple solution and extraction solvent by syringe for sev-

a conical test tube. After extraction, phase separation isby centrifugation, and the enriched analytes are deter-CFID. This method requires less volume of organic

does not use a disperser solvent. The extraction solvent by aspiration and expulsion of the sample mixture byead of using disperser solvent. It is simple, requires lit-solvent, and is suitable for extraction of various organic

in aqueous samples.

sound-assisted emulsicationnd-assisted [36,37] and vortex-assisted emulsicationuce the consumption of solvent. Regueiro et al. [36] andl. [37] developed USAEME for concentration of analytes.-assisted emulsication has been found to improve ef-ncreasing the rate of mass transfer between the two

phases. In 2008, Regueiro et al. developed a noveled on USAEME and GCMS for the analysis of syntheticnces (Fig. 4(a)) [36]. In their method, a 10 mL sample is15 mL conical-bottom glass centrifuge tube, and 5 ng ofte standard PCB-166 in acetone is added to the sam-L solution of 5 ng of PCB-195 (internal standard) in

is added as extractant. The tube is then immersed inic water bath (40 kHz ultrasound frequency and 100 W0 min at 25 3 C). The resulting emulsion is then dis-entrifugation and the organic phase is sedimented at

of the conical tube. Chloroform is removed by using a the remaining extract is transferred to a 100 L glass.8 mL GC vial. Extracts are stored at 20 C until analysis

USAEME is an efcient, simple, rapid, and inexpen-tive to other extraction techniques such as solid-phaseSPE), solid phase microextraction (SPME), and LPME. Aroach of extraction reported by Fontana et al. uses ultra-urfactant [39]. It is environmentally friendly because ofsumption of organic solvent.r, ultrasound-assisted emulsication for extendedy lead to decomposition of analytes. A number of reportshat the use of manual shaking in USAEME improveson efciency and lowers the ultrasonic extraction time,imizes decomposition of analytes [40,41]. Lin and Fuhound with occasional manual shaking to form a cloudy, and obtained good results [42]. Other fast and novelethods that use low-density solvent were developed by

[4345].

ctant-assisted emulsicationnt-assisted DLLME (SA-DLLME) [22,23] followed byeen developed for the extraction and determinationenols in environmental water samples (Fig. 4(b)). Inch, the cationic surfactant cetyltrimethylammonium


Table 3Extraction solvent and extraction time of different dispersion techniques.

Dispersion techniques Method Extraction solvent Extraction time (min) Ref

Manual shaking DLLME-LSC TCE 1.5 [34]Air-assisted emulsication AALLME Ultrasound-assisted emulsication USAEME Surfactant assisted emulsication SA-DLLME Vortex-assisted emulsication VALLME Low-density solvent-based vortex-assisted surfactant-enhanced-emulsication LDSVSLLME Vortex-assisted supramolecular solvent microextraction VASUSME Homogeneous ionic liquid microextraction HILME

bromide (CTAB) is used as a dispersing agent. An extraction sol-vent is injected rapidly into the aqueous sample containing CTAB,and the resulting mixture is shaken for 13 min to disperse theorganic phase. After extraction, the mixture is centrifuged and the

Fig. 4. Diagram

organic phative ultrasoand preconIn this metis conditionric acid (pHshaking of back-extracthe major dis also extravent; as a reanalytes. Liwith low coemulsion toconsequent[46].

2.1.5. VorteIn 2010

microextraThe analyteated mass (50 L) wasing the ionifor 2 min exphase wasassisted anof organic emulsicatwas fasterincreased tin fast and eemulsicatpose.

Zhang asurfactant-based on lothe samplesolvent tolutransferred

an etion,ed ansion to formtrifugacollectdisper of the extraction process of (a) USAEME, (b) VALLME, and (c) HLLE.

favors the mthe extractless than 1 of tradition

In 2013in manualtion, and uof dropletsanalytes wChloroform


emulsicatplete phase

2.1.6. MicroIn 2012

microwavetion of activSchisandra powder, 15([C4MIM][Bmicrowaveit was expothe vessel ihexauoropagent, is adtion of nein an emulare extractedeposits atFig. 5. Diagram of extraction by (a) MSPDDLLME

ion over-emulsied the mixture and resulted in incom- separation.

wave-assisted emulsication, homogeneous ionic liquid microextraction with-assisted emulsication was developed for the extrac-e constituents from fruits of Schisandra chinensis andsphenanthera [50]. In this method, 10 mg of sample0 L of 1-butyl-3-methylimidazolium tetrauoroborateF4]), and 10 mL of deionized water were combined in a

extraction vessel. After the sealed vessel was shaken,sed to microwave radiation at 200 W for 6 min. Afters cooled to ambient temperature, 0.8 g of ammoniumhosphate ([NH4][PF6]), which is used as an ion-pairingded. A cloudy mixture is formed because of forma-

droplets of [C4MIM][PF6] homogeneously dispersedsion. Upon formation of [C4MIM][PF6], the analytesd into the IL phase. After centrifugation, the IL phase

the bottom of the centrifuge tube. This method is

suitable foructs.

2.2. CombinDLLME

2.2.1. SolidSPE and

13 OPPs in alarge volumC18 (100 mdesired comcollected in(12 L) wasdrawn into in a screw-cthen centrianalysis. Thand short aand (b) D--SPE.

the extraction of active constituents in natural prod-

ation of techniques for extraction and analysis with

-phase extraction combined with DLLMEDLLME coupled with GC were used for determination ofqueous samples [51]. The analytes were collected fromes of aqueous solutions (100 mL) into the sorbent SPEg). The C18 SPE cartridge was used in separation of thepounds by elution with 1 mL of acetone. Eluates wereto a 10 mL screw-cap glass test tube. Chlorobenzene

added to the test tube and the resulting mixture wasa syringe and rapidly injected into double distilled waterap glass test tube with conical bottom. The mixture wasfuged and the extractant was injected into the GC foris method is fast and simple, and affords very high EFsnalysis time.


2.2.2. Stir bar sorptive extraction (SBSE) combined with DLLMESBSE combined with DLLME [52] has been developed for the

extraction of six triazole pesticides in aqueous samples. In thismethod, 100 mL of standard or sample solution is stirred with astir bar coatbar is subsetaining 1 mremoved, 2is added to injected intcentrifugedinto GC forsensitive de

2.2.3. Molecombined w

A MIM sapplied as aof four Sudbent was aMSPDDLLMby using smof the egg glass beaketransferred50 mg of MIthen elutedate was col1.0 mL. It wafurther purMIMMSPDMSPD, and

2.2.4. SuperSFE follo

tion and dewas performcollected intion solven(1.0 mL of ainto 5.0 mLthe sedimenthe applicagreat potensamples.

2.2.5. NanoDispersi

combined win environminjected ravial is subseand elutionadded to thticles are ustep. A magand isolate by decantatacetonitrilethe nanopanext to thedorf tube bynot requirewell as tedthe solvent

Recently, a simple and efcient two-step method, vortex-assisted micro-solid-phase extraction (VA--SPE) followed bydispersive liquidliquid microextraction based on low-densitysolvent (LDS-DLLME), was developed for the determination of

evel -SPE

nanwithdevied foced nd a

xtraclvenCl soxtraction.L mic

for ovel a

usecentn waE bynethuened thtion

her m

reseoomof oronvere, hilarityomprminironmsed ang le

t yextraped ethodater t doion genoThrorredyringted rocedliquugatn is

and tthert mif bomo9]. Hf oced with octadecyl silane for 30 min at 300 rpm. The stirquently removed and placed in a 1.5 mL glass vial con-L of methanol for liquid desorption. After the stir bar is5 L of the extraction solvent 1,1,2,2-tetrachloroethanethe extracted analytes. The resulting solution is rapidlyo 5 mL of sodium chloride solution by syringe and then. The sedimented organic phase is removed and injected

analysis. This method enables simple, selective, andtermination of analytes in complex matrixes.

cularly imprinted matrix solid-phase dispersionith DLLME (MIMMSPDDLLME)ynthesized by aqueous suspension polymerization was

selective sorbent for the simultaneous determinationan dyes in egg yolk samples (Fig. 5(a)) [53]. The sor-

miniaturized matrix solid-phase dispersion used forE. The miniaturized MSPD procedure was performed

all amounts of sample, support, and solvent. An aliquotyolk sample and MIM sorbent were placed in a smallr and blended together. The homogenized mixture was

to an empty cartridge (5 cm 8 mm i.d., prepacked withM), rinsed with 4.0 mL of methanolwater solution, and

with 3.0 mL of acetoneacetic acid solution. The elu-lected in a 10 mL conical tube and then evaporated tos then mixed with 100 L of TCE and 5.0 mL of water for

ication and concentration of analytes by DLLME. ThisDLLME method combined the advantages of MIM,DLLME.

critical uid extraction (SFE) combined with DLLMEwed by DLLME [54,55] has been developed for extrac-termination of PAHs in marine sediments. SFE of PAHsed at 313 K and 253.2 bar, and the extracted PAHs were

1 mL of acetonitrile. Subsequently, 16 L of the extrac-t chlorobenzene was added to the collecting solventcetonitrile). The resulting mixture was rapidly injected

of aqueous solution. After centrifugation, the PAHs inted phase were analyzed by GC. This procedure extends

tion of DLLME to solid samples. In particular, it holdstial in the analysis of trace organic compounds in solid

techniques combined with DLLMEve micro-solid-phase extraction (D--SPE) (Fig. 5(b))ith DLLME [56,57] was developed for GCMS of PAHsental samples. For the dispersion step, 1-octanol is

pidly into a vial containing sample solution and thequently sealed and vortexed. For SPE step (absorption), derivatized magnetic nanoparticles are then quicklye vial. In this approach, hydrophobic magnetic nanopar-sed to recover the extractant 1-octanol in the DLLMEnet is held next to the bottom of the vial to attract

the nanoparticles, and the sample solution is discardedion. The magnet is thereafter removed, and 100 L of

is introduced to the vial to desorb the 1-octanol fromrticles by sonication. Finally, the magnet is again placed

vial, and the supernatant is collected into an Eppen- an automatic pipettor for analysis. This procedure does

special apparatus such as conical-bottom test tubes asious procedures of centrifugation and refrigeration of. It also potentially lends itself to possible automation.

trace-lEach carbonbrane -SPE vortexand pla5 min anext etion so10% NaAfter etrifugaa 50 system

A non thepreconlytes iin LLMdodecathe toltion, anabsorp

2.3. Ot

At puse of rposed with cpressuand poganic cto detein envet al. ureduci[25].

Lasmicroedevelothis mand wsequenextract(homovent). transfemicrosis injecnew pliquidcentrifotatiowater

Anosolvention otetrabrrials [42 mL ophthalate esters in environmental water samples [58]. device was fabricated by packing 4 mg of multiwalledotubes in a 1.0 cm 0.8 cm porous polypropylene mem-

heat-sealed edges. In the rst step of VA--SPE, thece is placed in a 20 mL sample solution, which is thenr 6 min. After extraction, the -SPE device is removedin a glass insert. Analytes are desorbed by sonication forcetonitrile (350 L) is used as dispersing solvent in thetion (DLLME) step. In LDS-DLLME, a mixture of extrac-t and acetonitrile extract is rapidly injected into a 5 mLlution by plastic Pasteur pipette to form an emulsion.tion, the emulsion is separated into two phases by cen-

The organic extract is conveniently collected by usingrosyringe, and the extract is injected into the GCMS

analysis.nd highly efcient microextraction methodology based

of palladium nanoparticles was developed for theration and determination of Hg and other inorganic ana-ter samples [59]. Analytes were selectively separated

application of clusters protected by a monolayer ofiolate-coated Pd (C12S Pd MPCs). A 20 L portion of

phase containing C12S Pd MPCs was used for extrac-e nal phase was injected into an electrothermal atomicspectrometer for Hg detection.

ethods using low-toxicity solvent

nt, the development of extraction methods includes the-temperature ILs and surfactants. ILs are generally com-ganic cations and inorganic anions [6063]. Comparedntional organic extraction solvents, ILs have low vaporgh viscosity, good thermal stability, tunable miscibility, and good extractability with various organic and inor-ounds [63,64]. Therefore, application of ILs in DLLMEe many various types of contaminants and pesticidesental water samples have been reported [5775]. Ku

n up-and-down shaker and ILs to extract analytes whilevels of extracted ILs and the use of disperser solvent

ar, otation-assisted homogeneous liquidliquidction (FA-HLLME) followed by GCFID analysis wasfor the extraction of four PAHs in soil samples [76]. In, PAHs are extracted from soil samples into methanol(1:1, v/v) by using ultrasound, and ltration is sub-ne as a cleanup step. The ltrate is added into ancell, which contains a mixture of 1.0 mL of methanolus solvent) and 150.0 L of toluene (extraction sol-ugh N2 otation, the dispersed extraction solvent is

to the surface of the mixture and then collected bye. Subsequently, 2 L of the collected organic phaseinto the GCFID system for subsequent analysis. Thisure is different from the conventional homogeneous

id microextraction (HLLE) (Fig. 4(c)), as it does not needion to separate the organic phase. In this method, N2

used to break up the emulsion of organic solvent ino nish the extraction process.

new method, vortex-assisted supramolecularcroextraction, has been developed for determina-isphenol-A, 2,4-dichlorophenol, bisphenol-AF, andbisphenol-A in liquid foods and their packaging mate-ere, a supramolecular solvent is prepared by mixing

tylalcohol and 10 mL of tetrahydrofuran in 38 mL of


distilled water and 10 L of HCl (2 M). After the sample prepara-tion, 500 L of the supramolecular solvent as extraction solventis added into the sample, the mixture is vortexed for 2 min. Aftercentrifugation, the supramolecular solvent, which is less densethan water,and dilutedanalyzed by

3. DLLME a

DLLME iof sample, aorganic cominorganic anin the analyanimal tissupretreatme

3.1. Applica

3.1.1. OrganAfter DL

often beenmainly becin water anextraction ssolubility inmethod. Peby DLLME incides [78], m[81], carbamcides [83]. solvents. Hless-toxic ebenzoylure[C6MIM][PFanalysis of col [86], cleuoroquino[92], volatilBesides theame retardanilines [10[106], and that DLLMEorganic com

3.1.2. InorgDLLME h

a wide varifrom watercommon anused in theof metals fGrzeskowiavarious methe sampleare then exions are anafurnace atotively coupl[122,123]. Tassisted by

3.2. Application of DLLME to various eld samples

Before 2009, only a few papers describe the use of DLLME in theanalysis of analytes in food samples. Most of these works focus

ter sed rtamledg

mpoet al.cids er coo anpolyes [1

ple anlinf me

last tion

a lited fring [ave

solveandd ma

clus

ny D is aple

techLLMration, thds tof anxic ds, anoveoremof ortechny solds.bin

ex saith D

natiot or dnveseneples.using

nanundsnd mretrienal tionrt frds w forms the top layer of the mixture. It is then removed to 1.0 mL with acetonitrile, 10.0 L of the solution is

HPLC.

pplications

s simple, rapid, and inexpensive, requires low volumesnd affords high EF. It can be applied in the analysis ofpounds (pesticides, pharmaceuticals, and phenols) andalytes (Cu, Pb, and Cd). DLLME methods have been usedsis of various samples such water samples, food, urine,e or offal, soil, and leaves. DLLME is a popular sample

nt step in methods developed for analysis of food.

tion of DLLME for various analytes

ic compoundsLME has been introduced by Rezaee et al. [6], it has

used in the analysis of pesticides in water samplesause many highly toxic pesticides have low solubilityd high solubility in non-polar extraction solvents. Theolvent must have ability to extract target analytes, low

aqueous samples, and applicability to the analyticalsticides that are commonly analyzed upon extractionclude OPPs [77], triazole pesticides [52], triazine herbi-ethomyl [79], heterocyclic insecticides [80], fungicidesate pesticides [82], and n-methyl carbamate pesti-

These pesticides are extracted with toxic chlorinatedowever, other pesticides have been analyzed by usingxtraction solvents in water. For example, OPPs [84] anda pesticides have been extracted with hexadecane and6] [85], respectively. DLLME has also been applied to thepharmaceuticals, and phenols such as chlorampheni-nbuterol [87], inammatory drugs [88], lovastatin [89],lones [90], alkylphenol [91], bisphenol and bisphenol Be phenols [93], chlorophenols [94,95], PAHs [54,56,96].

above compounds, other organic compounds such asants and plasticizers [97102], aromatic amines [103],4], fatty acids [105], glycyrrhizic acid [20], parabens

antioxidants [107]. These above applications illustrate is suitable for use in extraction of different types ofpounds.

anic compoundsas been applied to the extraction and concentration ofety of organic compounds and metal ions [10], mainly

samples. After pesticides, metals are the second mostalytes that are extracted by DLLME. DLLME has been

last few years in the extraction and preconcentrationor analysis [31,33,108126]. Zgoa-Grzeskowiak andk summarized the DLLME methods for the analyses oftals [10]. In these methods, chelating agent is added to

to extract the metal ions. Ions from the liquid phasetracted to the extracting solvent as a complex. Finally,lyzed through appropriate techniques such as graphitemic absorption spectrometry [112,120,121,124], induc-ed plasma optical emission spectrometry [113], or FAAShe number of published studies on inorganic analysisDLLME may increase very rapidly in the near future.

on waincreasfor conacknowtain coBakar nolic a

Othprior t[146], in leav[148].

Samthe clebers oin theextracable inextracor stirrmicrowperserother hthe foo

4. Con

MaDLLMEin samDLLMEwith Dof opeadditiomethotypes oless tomethoOther the afumes these densitmetho

Comcompltions wcombisolvenrepay ihave bof sam

By face ofcompoticles aand to functioapplica

Apamethoamples or aqueous phases [127143]. Because of theegulation for food safety, the importance of analysisinants or other harmful substances has been greatlyed. Food matrixes are notoriously complex; they con-nents such as carbohydrates, lipids, and proteins [144].

used DLLME to extract vegetable oils containing phe-into an aqueous solution [145].mplex analytes for which DLLME is used for extractionalysis polychlorinated biphenyls in sh [102] and soilbrominated diphenyl ethers in animal tissue [147], Rh24], Cd in beverage and cereal [119], and Al in fruit juice

preparation can affect the analyte concentration andess of the sample prior to further analysis. The num-

thods that use a two-step preparation have increasedfew years. Solid samples generally require previouswith a suitable solvent to make the analytes avail-quid matrix [149]. In these methods, analytes may beom the food matrix with an organic solvent, by shaking102,147,150154], USE [155,156], SPE [81,154,156], or-assisted extraction [157]. A second step that uses a dis-nt is typically performed [81,102,147,150157]. On the, DLLME may be a cleanup step before extraction fromtrix.

ion

LLME methods have been developed in recent years. novel microextraction technique with great potentialpretreatment. This review introduces many novelniques, disperser techniques, and new combinationsE. Advantages of these techniques include simplicityn, low cost, rapid extraction, and great potential. Inis review illustrates the application of dispersion LPME

allow separation and preconcentration of variousalytes and samples. The rst section discusses varioussolvents that are successfully used to develop newnd many devices that were developed for DLLME.l online DLLME techniques were reported. Some ofentioned dispersion techniques use very low vol-ganic solvent or no dispersion solvent. Furthermore,iques may also be combined with DLLME with low-vent and high-density solvents to develop other new

ing other extraction methods with DLLME for analysis ofmples may be more effective and useful. Many combina-LLME have been reported, but not much is known aboutns of extraction methods with DLLME with low-toxicityispersion LPME. This direction of the research may welltigation. The above DLLME or dispersion LPME methodsts as cleanup and ltering steps to remove impurities

the new nanotechnique to assist extraction, the sur-oparticles can be modied to extract various organic

and solvents. For example, specially coated nanopar-agnetic nanoparticles may be used to assist extractionve the extraction solvent, respectively. Newly prepared

nanoparticle will extend the usages DLLME in variouss.om the combined methods, many traditional LPMEith no dispersing solvent or DLLME have been reported.


Among LPME methods, these have much potential for develop-ment. Some of the conventional DLLME methods were developed toobviate centrifugation and the use of disperser solvent or to lowerthe volume of the organic solvent used.

Finally, tminiaturizacost, labor, tdispersion Lfuture.

Conict of

The auth

Acknowled

This woTaiwan (NSour sincereing our reseduring the l

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interest

ors declare no conict of interest.

gments

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Beyond dispersive liquidliquid microextraction1 Introduction1.1 DLLME with lower-density extraction solvent1.1.1 DLLME based on solidification of floating organic droplet (DLLME-SFO)1.1.2 DLLME with special extraction devices1.1.3 Low-density-solvent based solvent demulsification DLLME (LDS-SD-DLLME)

1.2 DLLME with higher-density extraction solvent1.2.1 DLLME with low-toxicity solvent1.2.2 Auxiliary solvent to adjust the density of DLLME1.2.3 DLLME with automated online sequential injection

2 Development of DLLME2.1 Various techniques for assisting dispersion2.1.1 Manual shaking for assisting dispersion2.1.2 Air-assisted liquidliquid microextraction (AALLME)2.1.3 Ultrasound-assisted emulsification2.1.4 Surfactant-assisted emulsification2.1.5 Vortex-assisted emulsification2.1.6 Microwave-assisted emulsification

2.2 Combination of techniques for extraction and analysis with DLLME2.2.1 Solid-phase extraction combined with DLLME2.2.2 Stir bar sorptive extraction (SBSE) combined with DLLME2.2.3 Molecularly imprinted matrix solid-phase dispersion combined with DLLME (MIMMSPDDLLME)2.2.4 Supercritical fluid extraction (SFE) combined with DLLME2.2.5 Nanotechniques combined with DLLME

2.3 Other methods using low-toxicity solvent

3 DLLME applications3.1 Application of DLLME for various analytes3.1.1 Organic compounds3.1.2 Inorganic compounds

3.2 Application of DLLME to various field samples

4 ConclusionConflict of interestAcknowledgmentsReferences

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