ORIGINAL PAPER

In-situ ionic liquid-based microwave-assisted dispersiveliquid–liquid microextraction of triazine herbicides

Qiu Zhong & Ping Su & Yao Zhang & Ruoyu Wang &

Yi Yang

Received: 6 April 2012 /Accepted: 1 June 2012 /Published online: 14 June 2012# Springer-Verlag 2012

Abstract We report on the determination of the triazineherbicides ametryne, prometryne, terbuthylazine and terbu-tryn in water samples. The herbicides are extracted by in-situ ionic liquid-based microwave-assisted dispersive liquid-liquid microextraction and then determined by high-performance liquid chromatography. This is a newmethod for extraction that has the advantages of requir-ing less volume of ionic liquid (IL) than other methodsand at the same time is quite fast. The type and volumeof IL, the type and volume of disperser, irradiationtemperature, extraction time and salt concentration wereoptimized. Figures of merit include linear regressioncoefficients between 0.9992 and 0.9995, acceptable recover-ies (88.4–114 %), relative standard deviations of 1.6–6.2 %,and limits of detection between 0.52 and 1.3 μg L−1.

Keywords In-situ ionic liquid-based microwave-assisteddispersive liquid-liquid microextraction . Triazineherbicides .Water . High-performance liquidchromatography . Ionic liquid

Introduction

Triazine herbicides, which are heavily used in corn andsoybean production for the control of weeds, are ubiquitousenvironmental pollutants in water, soil and organisms. Their

mobility, solubility in water and moderate persistence hascaused great concern [1]. In European Union, the maximumallowed limit has been set at 0.1 μg L−1 for each individualherbicide and totally 0.5 μg L−1 in drinking water anddrinking water sources [2], but United States EnvironmentalProtection Agency has set the maximum contaminant levelof atrazine at 3 μg L−1 and simazine at 4 μg L−1 in drinkingwater [3]. Because of the fact that triazine herbicides areusually present at trace levels in water, there are higherdemands (high sensitivity, selectivity, and resolution power;high speed and efficiency; negligible volume of solventused and low experimental cost) on the analytical methods.As one of the trends in sample extraction technology is theelimination or minimization of toxic organic solvents [4], itis highly desirable that these analytical methods could alsobe environmental friendly “green” [5].

Common extraction methods have been utilized for theanalysis of triazine herbicides in water samples, includingliquid-liquid extraction (LLE) [6] and solid-phase extraction(SPE) [7, 8], which all consume long time and a largeamount of hazardous organic solvents. Subsequently, twotypes of solvent-free and convenient methods, solid-phasemicroextraction (SPME) [9, 10] and stir bar sorptive extrac-tion (SBSE) [11, 12], were reported for determination of thetriazine herbicides from water samples. But the extractiontime is at least 1 h, and the fibers of SPME and stir bars ofSBSE are both lifetime-limited and expensive. Recently, anovel dispersive liquid-liquid microextraction technique(DLLME) was developed for the extraction and analysis oftriazine herbicides from water samples [5]. Although thismethod is simple, rapid and inexpensive [13], there are stillmicroamount of hazardous organic solvents used as extractionand disperser solvent.

As considered to be a kind of “green” solvents, ionicliquids (ILs) are less obviously hazardous than conventional

Electronic supplementary material The online version of this article(doi:10.1007/s00604-012-0847-9) contains supplementary material,which is available to authorized users.

Q. Zhong : P. Su :Y. Zhang :R. Wang :Y. Yang (*)College of Science, Beijing University of Chemical Technology,15, Bei San Huan East Road,Beijing 100029, Chinae-mail: yangyi@mail.buct.edu.cn

Microchim Acta (2012) 178:341–347DOI 10.1007/s00604-012-0847-9

organic solvents and become an alternative. Based on tradi-tional DLLME, ILs replaced the conventional organic sol-vents and worked as the extraction solvents for theextraction of organophosphorus pesticides [14], DDT and itsmetabolites [15] and heterocyclic pesticides [16], while haz-ardous organic solvents are still applied as disperser solvents.Another IL-DLLMEmethod was carried out firstly by heatingto make ILs dissolved andmixed entirely with the sample, andthen the analyte was enriched into sedimented IL by coolingand centrifugation. This method has been utilized in the ex-traction of phthalate esters and pyrethroid pesticides [17],carbamate pesticides [18], organophosphorus pesticides [19],triazine and phenylurea herbicides [20]. However, it takes atleast 30 min for the heating and cooling process, and the entiretime of sample preparation is about 1 h. Anderson et al. [21]introduced a novel IL-DLLME method using an in situ me-tathesis reaction for the preconcentration of aromatic com-pounds from water. In the in-situ IL-DLLME approach, ahydrophilic IL is dissolved completely in the water sample,and an ion-exchange reagent as a disperser solvent is thenintroduced to form a turbid solution with hydrophobic ILmicrodroplets through the in situ metathesis reaction. As thismethod is very rapid and does not require an organic dispersersolvent, it has been used to determine 14 emerging contami-nants [22], four insecticides [23], and endocrine disruptingphenols [24] in several water samples. A similar approach, insitu solvent formation microextraction, was developed to de-termine mercury and cadmium in saline samples [25, 26]. Thepublished in-situ IL-DLLME methods were mostly carriedout by hand-shaking or vortex for 30 s-4 min. ConsideringILs can efficiently absorbmicrowave energy and thus are usedas solvents and co-solvents for microwave-assisted extraction[27], Wang and co-workers [28, 29] combined microwaveenergy and IL-DLLME for the derivatization and determina-tion of sulfonamides and formaldehyde from liquid samples,in which microwave can aid extraction and dispersion.

In this study, microwave was introduced into in-situ IL-DLLME method for the first time. The novel in-situ ionicliquid-based microwave-assisted dispersive liquid-liquidmicroextraction (in-situ IL-based MADLLME) was devel-oped for the preconcentration of four triazine herbicidesfrom water samples, followed by direct injection of the ILextract into HPLC. The effects of various experimentalparameters were studied and the optimized method wassuccessfully applied to the real water sample analysis.

Experimental

Chemicals

Ametryne, terbuthylazine and terbutryn standards were pro-vided by Bingzhou Pesticide Plant (Shandong, China),

while prometryne was supplied by Agro-Environmental Pro-tection Institute, Ministry of Agriculture (Tianjin, China,www.aepi.net.cn), as a stock solution at a concentration of100 mg L−1 in acetone. The synthesis-grade ILs, 1-butyl-3-methylimidazolium tetrafluoroborate ([C4MIM][BF4]), 1-hexyl-3-methylimidazolium tetrafluoroborate ([C6MIM][BF4]), 1-octyl-3-methylimidazolium tetrafluoroborate([C8MIM][BF4]), were purchased from Lanzhou GreenchemILS, LICP. CAS. (Gansu, China, www.ionicliquid.org). Po-tassium hexafluorophosphate (KPF6) and lithium bis[(tri-fluoromethane)sulfonyl]imide (LiNTf2) were purchasedfrom Cheng Jie Chemical Co. LTD (Shanghai, China,www.shyfhx.com). The acetonitrile of HPLC grade was fromJ&K Chemical LTD (Beijing, China, www.jkchemical.com).

Fig. 1 Effect of different ILs on the extraction efficiency of targetherbicides. Extraction conditions: 5 mL water sample; 40 μL IL;500 μL 0.2 gmL−1 LiNTf2 solution as disperser; 30 W microwavepower; 50 °C irradiation temperature; 90 s extraction time

Fig. 2 Effect of the volume of [C4MIM][BF4] on the extractionefficiency of target herbicides. Extraction conditions: 5 mL watersample; 0.2 gmL−1 LiNTf2 solution; 30 W microwave power; 50 °Cirradiation temperature; 90 s extraction time

342 Q. Zhong et al.

Ultrapure water was prepared in the lab by a water treatmentdevice. All other chemical reagents used in the experimentwere of analytical grade.

A mixed standard solution containing each analyte at4 mg L−1 was prepared in acetone and stored at 4 °C. ILs,the mixed standard solution, KPF6 and LiNTf2 solutionwere filtered through a 0.45 μm filter membrane beforethe extraction procedure, respectively. The spiked watersamples were prepared daily by diluting the mixed standardsolution in the ultrapure water and used in the experiments.The concentration of each triazine herbicide in the spikedsamples was 40 μg L−1. Tap water, spring water and bottleddrinking water were collected and stored, and filteredthrough a 0.45 μm filter membrane before extraction.

Apparatus

The extraction was performed by a Discover SP microwaveextraction apparatus from CEM experimenting company(Matthews, NC, USA, www.cem.com). The Agilent 1100series liquid chromatograph (Palo Alto, CA, USA,www.agilent.com) equipped with an ultraviolet detectorwas used. Chromatographic separation of target analytes wasperformed on Eclipse XDB-C18 column (4.6 mm×150 mm,

5 μm) (Agilent, Palo Alto, CA, USA). A H2050RHigh-SpeedRefrigerated Tabletop Centrifuge (Xiang Yi Centrifuge Instru-ment Co. LTD, Hunan, China, www.lxjxy.com) was used forsample treatment.

In-situ ionic liquid-based microwave-assisted dispersiveliquid-liquid microextraction procedure

A 10-mL microwave tube was filled with 5 mL water sample.Then, 40 μL IL was injected into the sample using a 100-μLsyringe. The IL was completely dissolved into the watersample after gentle shaking by hand for 1 min. A cloudysolution was formed as soon as 500 μL 0.2 gmL−1 LiNTf2solution was added. Then the suspension was immediatelyirradiated under the microwave power of 30 Wand the irradi-ation temperature of 50 °C for 90 s. After cooling to roomtemperature, the suspension was centrifuged at 5,000 rpm for6 min. After centrifugation, the upper aqueous phase wasremoved completely, and the IL phase, settled on the bottomof the tube, was stored for HPLC analysis. All extractionexperiments were performed in triplicate.

Chromatographic conditions

The flow rate of mobile phase was kept at 1 mL min−1. Themobile phases were acetonitrile and water, respectively. Thegradient started with 45 % acetonitrile and was slowlyincreased to 50 % over 20 min. Sample injection volumewas 5 μL and the wavelength of ultraviolet detector was setat 223 nm.

Results and discussion

Optimization of in-situ ionic liquid-basedmicrowave-assisted dispersive liquid-liquidmicroextraction

In order to optimize the in-situ IL-based MADLLME, theinfluence of experimental parameters, including the type andvolume of ILs, type and volume of disperser, irradiationtemperature, extraction time and salt concentration, was in-vestigated. Extraction efficiency was represented as the

Table 1 Analytical performances

Compound Linear range(μg L–1)

Slope±SD Intercept±SD R2 LOD(μg L−1)

LOQ(μg L−1)

Ametryne 2.5–100 6.292±0.126 −7.828±5.926 0.9992 1.3 4.4

Terbuthylazine 2.5–100 5.310±0.084 −4.309±3.962 0.9995 0.94 3.1

Prometryne 2.5–100 5.705±0.109 −2.408±5.125 0.9993 0.52 1.8

Terbutryn 2.5–100 6.707±0.124 −7.153±5.846 0.9993 0.69 2.3

Fig. 3 Effect of irradiation temperature on the extraction efficiency oftarget herbicides. Extraction conditions: 5 mL water sample; 40 μL[C4MIM][BF4]; 500 μL 0.2 gmL−1 LiNTf2 solution as disperser; 30 Wmicrowave power; 90 s extraction time

Microextraction of triazine herbicides 343

revised peak areas calculated by multiplying the peak areaobtained with the volume ratio of sedimented IL to injectedIL.

Selection of ionic liquid

Characteristics of ILs, such as solubility in water, the viscosity,extraction capacity and chromatographic behaviour, play akey role in influencing the recovery and enrichment factor[30]. As a water-immiscible IL with very low solubility mustbe formed after the in-situ IL-based MADLLME procedure,the IL used must be liquid, water-miscible and inexpensive[25], leaving only 1-alkyl-3-methylimidazolium-type ILs con-taining PF6

− and BF4− for selection. As for triazines, the

extraction capacity of IL with the anion BF4− is stronger than

IL with the anion PF6− according to a previous work [31],

three kinds of ILs with different alkyl chain lengths, includ-ing [C4MIM][BF4], [C6MIM][BF4], and [C8MIM][BF4],were investigated in this study. The chromatographicpeaks of ametryne and terbuthylazine were completelyobscured by interference peaks when [C8MIM][BF4]was used, while the contrast of the extraction efficiencyof [C4MIM][BF4] and [C6MIM][BF4] was shown inFig. 1. The results indicated that the extraction efficiencyobtained with [C4MIM][BF4] was higher than those obtainedwith [C6MIM][BF4], so [C4MIM][BF4] was selected as thewater soluble IL to conduct in-situ IL-based MADLLME.

Selection of disperser

As ILs containing PF6− and NTf2

− are excellent hydropho-bic extractants, KPF6 and LiNTf2 were selected as disperser.

The equimolar amounts of the disperser were added, butno IL phase was observed at the bottom of the tubeafter centrifugation when KPF6 solution was used. Thatmay result from the higher solubility of [C4MIM][PF6]in water (1.88 g/100 mL) than those of [C4MIM][NTf2](0.80 g/100 mL) and the lower viscosity of [C4MIM][PF6](148–450 mPa s at 25 °C) than those of [C4MIM][NTf2](52 mPa s at 20 °C) [32]. Thus, LiNTf2 were selected asdisperser for the further experiments.

Effect of the volume of disperser

The volume of LiNTf2 solution can significantly affectthe amount of [C4MIM][NTf2] obtained by in-situ IL-based MADLLME. When the volume of [C4MIM][BF4]was 40 μL, and the concentration of LiNTf2 solutionwas 0.2 gmL−1, the extractions were carried out with differentdisperser volumes (200 μL, 350 μL, 500 μL, and 650 μL) toevaluate the effect on the extraction efficiency. The results,shown in Electronic Supplementary Material Fig. S1, indicat-ed that extraction efficiency of four herbicides increased whenthe volume of LiNTf2 solution increased from 200 μL to500 μL, but decreased when the volume increased from500 μL to 650 μL. That may be because the volume ofsedimented IL increased before the volume of LiNTf2 solutionreached 500 μL. The addition of more LiNTf2 did not makethe volume of sedimented IL increased, but greatly increasedthe viscosity of the solution which may make it more difficultfor target analytes molecules to diffuse into the IL extractionphase [21]. Therefore, when the volume of [C4MIM][BF4]was 40 μL, 500 μL LiNTf2 solution was used as disperser forfurther experiments.

Effect of the volume of ionic liquid

The extraction efficiency is affected by the amount of sedi-mented IL, which is determined by the volume of [C4MIM][BF4]. The smaller the volume of obtained [C4MIM][NTf2] is,the higher the concentrations of triazines are. However, quite asmall amount of IL caused the extraction to become difficultand insufficient, which may reduce precision and reproduc-ibility [24, 33]. Conversely, although more [C4MIM][NTf2]

Table 3 Comparison with other methods for triazines in water

Methods (compounds) Sample volume (mL) Extraction time (min) LOD (μg L−1) Recovery (%) RSD (%) Ref.

SPE-HPLC-UV (ametryne) 250 > 90 0.034 97.4 0.2 [8]

SPME-GC-MS (all four triazines) 1.2 60 0.010–0.014 − 2.1–4.5 [10]

SBSE-GC-MS (terbuthylazine) 20 60 0.0003 98.7 3.2 [12]

DLLME-GC-MS (prometryne) 5 3 0.046 115.6 4.86 [5]

IL-DLPME-HPLC-DAD (prometryne) 10 30 0.46 76.8 6.80 [20]

This proposed method (all four triazines) 5 1.5 0.52–1.3 88.4–114 1.6–6.2 –

Table 2 Recoveries, RSDs and EFs of the proposed method withspiked level of 40 μg L−1 (n05)

Compound Average recovery (%) RSD (%) EF

Ametryne 91.3 3.4 106

Terbuthylazine 88.4 1.6 103

Prometryne 114 5.3 132

Terbutryn 94.3 6.2 110

344 Q. Zhong et al.

may redound to higher extraction efficiency, it can also lead tolower preconcentration and higher limits of detection. In orderto investigate the influence of the volume of dissoluble IL onthe extraction efficiency, different volumes of [C4MIM][BF4](30, 40, 50, and 60 μL) were used when the molar ratio ofLiNTf2/[C4MIM][BF4] was kept constant. Figure 2 showedthat the extraction efficiency of four herbicides increasedwhen the volume of [C4MIM][BF4] increased from 30 μL to40 μL, and remained almost constant at the other volumelevels. Thus, a [C4MIM][BF4] volume of 40 μL was chosenin further experiments.

Effect of irradiation temperature and extraction time

The irradiation temperature controls the amount of energysupplied to the sample, affects chemical interactions and thekinetic reaction rate, and controls the partition of analytesbetween the sample and extractant [34]. But there is no clearagreement on the effect of temperature on the in-situ IL-DLLME procedures in the published reports, Shemirani etal. and Pino et al. [26, 35] were all inclined that the in-situIL-DLLME should be carried out under low temperature(such as 0 °C and room temperature) due to the low solubilityof IL. In this work, extractions were carried out at irradiationtemperatures of 40 °C, 50 °C, 60 °C and 70 °C, respectively.The results were shown in Fig. 3. The extraction efficiency offour herbicides increased when the irradiation temperatureincreased from 40 °C to 50 °C, but decreased at higherirradiation temperatures. These results were accordant withthe interesting extraction mechanism of in-situ IL-DLLMEpresented by Row et al. [33], which mentioned that someanalytes were removed from the aqueous phase by the hydro-phobic IL during its formation, and the remaining requiredenergy and time to distribute into the sedimented IL.When theirradiation temperature increased from 40 °C to 50 °C, moreanalytes distributed into the sedimented IL, when the temper-ature was higher, the volume of sedimented IL did not changesignificantly, but part of analytes released from the IL phase,leading to lower extraction efficiency. Therefore, 50 °C wasselected for further experiments.

Under microwave power of 30 W and irradiation tempera-ture of 50 °C, extractions were carried out for 0 s, 30 s, 60 s,90 s and 120 s to optimize the extraction time. Electronic

Supplementary Material Fig. S2 indicated that the extractionefficiency of the four herbicides increased dramatically from 0 sto 90 s, but decreased when the time exceeded 90 s, as heatingfor long time may lead to heat generated under microwaveirradiation. Thus, 90 s was chosen for further experiments.

Effect of salt concentration

The addition of salt is widely used in microextraction meth-ods as it often improves the analyte’s partitioning into theorganic extraction phase [21]. NaCl was chosen in order tostudy the effect of salt concentration on the extraction effi-ciency, and various experiments were performed by addingdifferent amounts of NaCl from 0 to 20 % (w/v). The resultsindicated that the extraction efficiency decreased with in-creasing salt content for all target triazines herbicides. Thepossible reasons for this behavior are similar to the additionof excessive LiNTf2, which was that the adding salt greatlyincreased the viscosity of the sample solution. Thus, saltwas not added to the sample in all subsequent experiments.

Evaluation of method performance

The in-situ IL based-MADLLME method was evaluated bylinear range, calibration linearity, limit of detection (LOD)

Table 4 Recoveries and RSDsof the triazines in real watersamples at a spiked level of40 μg L−1 (n05)

Analytes Tap water Spring water Bottled drinking water

Recoveries (%) RSD (%) Recoveries (%) RSD (%) Recoveries (%) RSD (%)

Ametryne 91.4 1.7 90.9 2.5 92.5 2.4

Terbuthylazine 92.1 4.3 90.3 2.7 96.8 2.0

Prometryne 102 3.2 106 2.8 106 2.2

Terbutryn 89.8 3.1 92.4 3.3 96.2 1.9

Fig. 4 Chromatograms of real (a) and spiked (b) water samples: (1)ametryne; (2) terbuthylazine; (3) prometryne and (4) terbutryn

Microextraction of triazine herbicides 345

and limit of quantification (LOQ) under the optimized con-dition. All the results were shown in Table 1. Calibrationcurves of each analyte were observed in the range of 2.5–100 μg L−1 with six concentration levels for all triazines.The correlation coefficient (R2), ranging from 0.9992 to0.9995, indicated good linearity of this method. The LODsand LOQs were calculated from signal-to-noise (S/N) ratiosof 3 and 10 at the lowest sample concentration, respectively.The LODs and LOQs for the analytes ranged from 0.52 to1.3 μg L−1 and 1.8 to 4.4 μg L−1, respectively. To evaluatethe precision of the proposed in-situ IL based-MADLLMEmethod, five replicates of ultrapure water spiked at a con-centration level of 40 μg L−1 were conducted. As shown inTable 2, the average recoveries and relative standard devia-tions (RSDs) of four triazines were in the range of 88.4–114 % and 1.6–6.2 %, respectively, and the enrichmentfactors (EFs) ranged from 103 to 132. These results indicatethat the optimized method provides acceptable recoveries andprecision for the determination of selected triazine herbicidesin water samples and has good capacity of enrichment.

Comparison of the developed method with other methods

The optimized in-situ IL-based MADLLME method was com-pared to some other methods with extraction for triazines inwater, which was shown in Table 3. The sample volume of thisoptimized method is smaller (5 mL) than other methods (exceptSPME), and the extraction time is especially less (1.5 min)compared with SPE, SPME, SBSE and IL-DLPME. By con-sidering the time of preparation of spiked sample (0.5 min), IL-dissolving (1 min), extraction (1.5 min) and centrifugation(6 min), all the time is about 10 min before injection into HPLC,which proves that the in-situ IL-based MADLLME is moreefficient. On the other hand, compared with other extractionprocedures in combination with HPLC, the LODs, recoveriesand RSDs obtained by the optimized method are acceptable.Because there is no volatile organic solvent used, this in-situ IL-based MADLLME method is environmentally friendly.

Analysis of real water samples

The optimized extraction method was applied to the analysisof three real water samples, including tap water, springwater and bottled drinking water. As the triazines in thewater samples are not detectable, the recoveries and RSDswere determined at a spiked level of 40 μg L−1. As shown inTable 4, the recoveries and RSDs were in the range of 89.8–106 % and 1.7–4.3 %, respectively. These results indicate thatthe matrix complexity had little interference on the in-situ IL-based MADLLME method. Thus, this method can be widelyused for the preconcentrations of triazine herbicides in watersamples. The chromatograms of the blank and spiked bottleddrinking water samples are shown in Fig. 4.

Conclusions

In this work, microwave technology was firstly introducedinto the in-situ ionic iquid-dispersive liquid-liquid micro-extraction procedure. This in-situ IL-based MADLLME-HPLC method, which was optimized by univariate analysis,was successfully applied to analyze four triazine herbicidesin water samples. The developed method is time-saving(about 10 min before injection into HPLC), efficient (aver-age recoveries from 88.4 % to 114 %) and environmentallyfriendly (no volatile organic solvents were used). The in-situIL-based MADLLME may be widely applied in the deter-mination of other compounds from environmental aqueoussample in future.

Acknowledgements This work was supported by the NationalNatural Science Foundation of China (NSFC No. 21075008 and90713013) and the Fundamental Research Funds for the CentralUniversities (ZD0904).

References

1. Spalding RF, Watts DG, Snow DD, Cassada DA, Exner ME,Schepers JS (2003) Herbicide loading to shallow ground waterbeneath Nebraska’s Management Systems Evaluation Area. J En-viron Qual 32:84

2. EC Drinking Water Guideline (1998) 98/83/CE. Brussels3. EPA Drinking Water Standards and Health Advisories (2004) EPA

822-R-04-005. Washington DC4. Armenta S, Garrigues S, de la Guardia M (2008) Green analytical

chemistry. Trends Anal Chem 27(6):4975. Nagaraju D, Huang S-D (2007) Determination of triazine herbi-

cides in aqueous samples by dispersive liquid–liquid microextrac-tion with gas chromatography–ion trap mass spectrometry. JChromatogr A 1161:89

6. Sabik H, Jeannot R (1998) Determination of organonitrogen pes-ticides in large volumes of surface water by liquid–liquid andsolid-phase extraction using gas chromatography with nitrogen–phosphorus detection and liquid chromatography with atmosphericpressure chemical ionization mass spectrometry. J Chromatogr A818:197

7. Loos R, Niessner R (1999) Analysis of atrazine, terbutylazine andtheir N-dealkylated chloro and hydroxy metabolites by solid-phaseextraction and gas chromatography–mass spectrometry and capil-lary electrophoresis–ultraviolet detection. J Chromatogr A 835:217

8. Pinto GMF, Jardim ICSF (2000) Use of solid-phase extraction andhigh-performance liquid chromatography for the determination oftriazine residues in water: validation of the method. J ChromatogrA 869:463

9. Valor I, Pérez M, Cortada C, Apraiz D, Moltó JC, Font G (2001)SPME of 52 pesticides and polychlorinated biphenyls: extractionefficiencies of the SPME coatings poly(dimethylsiloxane), poly-acrylate, poly(dimethylsiloxane)-divinylbenzene, Carboxenpoly(dimethylsiloxane), and Carbowaxdivinylbenzene. J Sep Sci 24:39

10. Frías S, Rodríguez MA, Conde JE, Pérez-Trujillo JP (2003) Opti-misation of a solid-phase microextraction procedure for the deter-mination of triazines in water with gas chromatography–massspectrometry detection. J Chromatogr A 1007:127

11. León VM, Álvarez B, Cobollo MA, Muñoz S, Valor I (2003) Analysis of 35 priority semivolatile compounds in water by stir bar

346 Q. Zhong et al.

sorptive extraction–thermal desorption–gas chromatography–massspectrometry I. method optimisation. J Chromatogr A 999:91

12. Sanchez-Ortega A, Unceta N, Gómez-Caballero A, Sampedro MC,Akesolo U, Goicolea MA, Barrio RJ (2009) Sensitive determina-tion of triazines in underground waters using stir bar sorptiveextraction directly coupled to automated thermal desorption andgas chromatography–mass spectrometry. Anal Chim Acta 641:110

13. Han DD, Row KH (2012) Trends in liquid-phase microextraction,and its application to environmental and biological samples.Microchim Acta 176:1

14. He LJ, Luo XL, Xie HX, Wang CJ, Jiang XM, Lu K (2009) Ionicliquid-based dispersive liquid–liquid microextraction followedhigh-performance liquid chromatography for the determination oforganophosphorus pesticides in water sample. Anal Chim Acta655:52

15. Zhao RS, Zhang LL, Wang X (2011) Dispersive liquid-phasemicroextraction using ionic liquid as extractant for the enrichmentand determination of DDT and its metabolites in environmentalwater samples. Anal Bioanal Chem 399:1287

16. Liu Y, Zhao EC, Zhu WT, Gao HX, Zhou ZQ (2009) Determina-tion of four heterocyclic insecticides by ionic liquid dispersiveliquid–liquid microextraction in water samples. J Chromatogr A1216:885

17. Zhou QX, Zhang XG, Xie GH (2011) Simultaneous analysis ofphthalate esters and pyrethroid insecticides in water samples bytemperature-controlled ionic liquid dispersive liquid-phase micro-extraction combined with high-performance liquid chromatogra-phy. Anal Methods 3:1815

18. Zhou QX, Pang L, Xiao JP (2011) Ultratrace determination of carba-mate pesticides in water samples by temperature controlled ionic liquiddispersive liquid phase microextraction combined with high perfor-mance liquid phase chromatography. Microchim Acta 173:477

19. Zhou QX, Bai HH, Xie GH, Xiao JP (2008) Trace determination oforganophosphorus pesticides in environmental samples bytemperature-controlled ionic liquid dispersive liquid-phase micro-extraction. J Chromatogr A 1188:148

20. Wang SL, Ren LP, Liu CY, Ge J, Liu FM (2010) Determination offive polar herbicides in water samples by ionic liquid dispersiveliquid-phase microextraction. Anal Bioanal Chem 397:3089

21. Yao C, Anderson JL (2009) Dispersive liquid–liquid microextrac-tion using an in situ metathesis reaction to form an ionic liquidextraction phase for the preconcentration of aromatic compoundsfrom water. Anal Bioanal Chem 395:1491

22. Yao C, Li TH, Twu P, Pitner WR, Anderson JL (2011) Selectiveextraction of emerging contaminants from water samples by dis-persive liquid–liquid microextraction using functionalized ionicliquids. J Chromatogr A 1218:1556

23. Li SQ, Gao HX, Zhang JH, Li YB, Peng B, Zhou ZQ (2011)Determination of insecticides in water using in situ halide ex-change reaction-assisted ionic liquid dispersive liquid–liquid

microextraction followed by highperformance liquid chromatogra-phy. J Sep Sci 34:3178

24. López-Darias J, Pino V, Ayala JH, Afonso AM (2011) In-situ ionicliquid-dispersive liquid-liquid microextraction method to deter-mine endocrine disrupting phenols in seawaters and industrialeffluents. Microchim Acta 174:213

25. Baghdadi M, Shemirani F (2009) In situ solvent formation micro-extraction based on ionic liquids: a novel sample preparationtechnique for determination of inorganic species in saline solu-tions. Anal Chim Acta 634:186

26. Mahpishanian S, Shemirani F (2010) Preconcentration procedureusing in situ solvent formation microextraction in the presence ofionic liquid for cadmium determination in saline samples by flameatomic absorption spectrometry. Talanta 82:471

27. Hoffmann J, Nüchter M, Ondruschka B, Wasserscheid P (2003)Ionic liquids and their heating behaviour during microwave irradi-ation—a state of the art report and challenge to assessment. GreenChem 5:296

28. Xu X, Su R, Zhao X, Liu Z, Zhang YP, Li D, Li XY, Zhang HQ,Wang ZM (2011) Ionic liquid-based microwave-assisted dispersiveliquid–liquid microextraction and derivatization of sulfonamides inriver water, honey, milk, and animal plasma. Anal Chim Acta707:92

29. Xu X, Su R, Zhao X, Liu Z, Li D, Li XY, Zhang HQ, Wang ZM(2011) Determination of formaldehyde in beverages usingmicrowave-assisted derivatization and ionic liquid-based disper-sive liquid–liquid microextraction followed by high-performanceliquid chromatography. Talanta 85:2632

30. Gao SQ, You JY, Zheng X, Wang Y, Ren RB, Zhang R, BaiYP, Zhang HQ (2010) Determination of phenylurea and triazineherbicides in milk by microwave assisted ionic liquid micro-extraction high-performance liquid chromatography. Talanta82:1371

31. Zhong Q, Su P, Zhang Y, Wang RY, Yang Y (2012) Ionic liquidbased microwave-assisted extraction of triazine and phenylureaherbicides from soil samples. Anal Methods 4:983

32. Liu JF, Jönsson JÅ, Jiang GB (2005) Application of ionic liquidsin analytical chemistry. Trends Anal Chem 24(1):20

33. Bi WT, Tian ML, Row KH (2011) Ultrasonication-assisted extrac-tion and preconcentration of medicinal products from herb by ionicliquids. Talanta 85:701

34. Cheng JH, Liu M, Zhang XY, Ding L, Yu Y, Wang XP, Jin HY,Zhang HQ (2007) Determination of triazine herbicides in sheepliver by microwave-assisted extraction and high performance liq-uid chromatography. Anal Chim Acta 590:34

35. Germán-Hernándeza M, Pino V, Anderson JL, Afonso AM (2012)A novel in situ preconcentration method with ionic liquid-basedsurfactants resulting in enhanced sensitivity for the extraction ofpolycyclic aromatic hydrocarbons from toasted cereals. J Chroma-togr A 1227:29

Microextraction of triazine herbicides 347