Effervescence-assisted dispersive liquid-liquid microextraction using a solid effervescent agent as...

J. Sep. Sci. 2014, 37, 3157–3163 3157

Wenqing Jiang1

Xiaochu Chen1

Fengmao Liu1

Xiangwei You1,2

Jiaying Xue1

1College of Science, ChinaAgricultural University, Beijing,P. R. China

2Tobacco Research Institute,Chinese Academy ofAgricultural Sciences, Qingdao,P. R. China

Received June 27, 2014Revised August 1, 2014Accepted August 2, 2014

Research Article

Effervescence-assisted dispersiveliquid–liquid microextraction usinga solid effervescent agent as a noveldispersion technique for the analysisof fungicides in apple juice

A novel effervescence-assisted dispersive liquid–liquid microextraction method has beendeveloped for the determination of four fungicides in apple juice samples. In this method, asolid effervescent agent is added into samples to assist the dispersion of extraction solvent.The effervescent agent is environmentally friendly and only produces an increase in theionic strength and a negligible variation in the pH value of the aqueous sample, which doesnot interfere with the extraction of the analytes. The parameters affecting the extractionefficiency were investigated including the composition of effervescent agent, effervescentagent amount, formulation of effervescent agent, adding mode of effervescent agent, typeand volume of extraction solvent, and pH. Under optimized conditions, the method showed agood linearity within the range of 0.05–2 mg/L for pyrimethanil, fludioxonil, and cyprodinil,and 0.1–4 mg/L for kresoxim-methyl, with the correlation coefficients >0.998. The limitsof detection for the method ranged between 0.005 and 0.01 mg/L. The recoveries of thetarget fungicides in apple juice samples were in the range of 72.4–110.8% with the relativestandard deviations ranging from 1.2 to 6.8%.

Keywords: Effervescence-assisted dispersion / Fungicide residues / High-performance liquid chromatography / JuiceDOI 10.1002/jssc.201400695

� Additional supporting information may be found in the online version of this articleat the publisher’s web-site

1 Introduction

Sample preparation, which aims at the isolation and/or pre-concentration of analytes from samples, represents a majorchallenge and crucial step in the development of an analyti-cal method. Conventional pretreatment methods such as LLEand SPE are time consuming and labor intensive, and requirelarge amounts of organic solvents. To overcome these draw-backs, many miniaturized extraction methods have been de-veloped recently, such as SPME [1] and LPME [2]. However, along extraction time is still required to obtain good extractionefficiency.

Correspondence: Professor Fengmao Liu, College of Science,China Agricultural University, Beijing 100193, P.R. ChinaE-mail: [email protected]: +86-10-62733620

Abbreviations: DLLME, dispersive liquid–liquid microextrac-tion; EADLLME, effervescence-assisted dispersive liquid–liquid microextraction; EF, enrichment factor; MRL,maximum residue limit; USAEME, ultrasound-assisted emul-sification microextraction

In 2006, Rezaee et al. demonstrated a novel microextrac-tion technique known as dispersive liquid–liquid microex-traction (DLLME) [3]. In conventional DLLME, the water-immiscible extraction solvent is dispersed into the aqueoussample solution in the form of fine droplets with the assis-tance of a water-miscible disperser solvent. The large surfacearea of the fine extraction droplets improves the rate of par-titioning of analytes between phases, and thus, enhances theextraction enrichment remarkably. However, the presenceof a relatively high volume (usually in the mL level) of dis-perser solvent may increase the solubility of target analytesin aqueous phase, which leads to low extraction efficiency. Inaddition, using a relatively high volume of organic solvent asdisperser solvent is environmentally unfriendly.

To overcome this disadvantage, various techniques forassisting dispersion such as manual shaking, ultrasound,vortex, and surfactants have been applied in DLLME [4–11].Regueiro et al. developed a novel method termed ultrasound-assisted emulsification microextraction (USAEME) for theanalysis of synthetic musk fragrances [4]. Vortex-assisteddispersive liquid–liquid microextraction was introduced byYiantzi and Psillakis for the analysis of pesticides in wa-ter [5]. Farajzadeh and Mogaddam developed an air-assisted

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3158 W. Jiang et al. J. Sep. Sci. 2014, 37, 3157–3163

liquid–liquid microextraction method for the extraction andpreconcentration of phthalate esters from aqueous samples[6]. Hu et al. reported a surfactant-assisted dispersive liquid–liquid microextraction for the determination of chlorophenolsin environmental water samples [7]. However, without the useof an organic disperser solvent, the time needed in microex-traction procedure can be much longer. In USAEME, analytedegradation may occur during the ultrasound process. In ad-dition, the use of the surfactants is limited in the chromatog-raphy system because of their strong UV absorbency [12] andhigh viscosity [13, 14].

Effervescence has been successfully applied to assist thedispersion of sorbents in dispersive micro-SPE [15, 16]. In2014, Lasarte-Aragones et al. introduced effervescent reac-tions into DLLME [17]. In the extraction procedure, sodiumcarbonate, as carbon dioxide source, was previously addedinto the aqueous sample. Subsequently, an extraction mix-ture (containing extractant and acetic acid as effervescenceprecursor) was slowly added to the sample by means of a sy-ringe, placing the needle at the bottom of the vial. In thisway, the effervescence occurred from down to the top ofthe vial and the extractant was homogeneously distributedinto the sample. This method is very rapid, effective, andreproducible. However, this method is not feasible for thedetermination of analytes that are unstable under alkalineconditions.

Fungicides have been widely used for pre- and posthar-vest treatments in fruits to control diseases [18]. The unde-sirable fungicide residues can remain on fruits and transferto processed products, such as juices [19]. To date, althoughfew maximum residue limits (MRLs) for the target fungi-cides have been established in juices, the MRLs have beenestablished in raw fruits. The MRLs in apples established bythe European Union for pyrimethanil, fludioxonil, cyprodinil,and kresoxim-methyl are respectively 7, 5, 1, and 0.2 mg/kg.The evaluation of fungicide residues in fruit juice samplesis a priority objective to ensure food quality and protect con-sumers against possible health risks. Hence, the developmentof analytical methods for determination of fungicide residuesin juice samples is of great importance.

In this paper, a novel effervescence-assisted dispersiveliquid–liquid microextraction (EADLLME) method, whichemploys a solid effervescent agent to assist the dispersionof extraction solvent, has been developed for the determina-tion of fungicides in aqueous samples. The proposed methodgives good extraction efficiency without using disperser sol-vent. When the effervescent reaction finishes, the final prod-uct only produces an increase in the ionic strength and anegligible variation in the pH value of the aqueous sam-ple, which does not interfere with the extraction of the tar-get analytes. Some experimental parameters, including thecomposition of effervescent agent, amount of effervescentagent, formulation of effervescent agent, adding mode of ef-fervescent agent, type of extraction solvent, volume of extrac-tion solvent, and effect of pH have been investigated andoptimized.

2 Materials and methods

2.1 Reagents and materials

The standards of pyrimethanil (99.5%), fludioxonil (97.5%),cyprodinil (99.0%), and kresoxim-methyl (98.5%) were pur-chased from Agricultural Environmental Protection Insti-tution of Tianjin (Tianjin, China). The analytical reagentsof sodium bicarbonate (NaHCO3), sodium carbonate(Na2CO3), potassium bicarbonate (KHCO3), potassium car-bonate (K2CO3), sodium dihydrogen phosphate (NaH2PO3),citric acid (C6H8O7), sodium hydroxide (NaOH), hydrochlo-ric acid (HCl), chlorobenzene (C6H5Cl), carbon tetrachloride(CCl4), and chloroform (CHCl3) were purchased from theBeijing Chemical Reagents Company (Beijing, China). Ultra-pure water was purified in a Milli-Q water purification system(Millipore, USA). Samples of apple juice (Weiquan Brand,China) were purchased from a local supermarket.

Stock solutions were prepared in acetonitrile and storedat −20�C. Working standards were prepared daily by dilutingthe stock solutions with ultra-pure water.

2.2 Effervescent agent preparation

2.2.1 Effervescent powder preparation

Citric acid (0.42 g) and potassium carbonate (0.276 g) weremixed and manually blended in a mortar until a homoge-neous and fine powder was obtained. The effervescent powdercould be immediately used for extraction or be compressedto a tablet.

2.2.2 Effervescent tablet preparation

An accurately weighed amount of 0.696 g of effervescent pow-der was compressed in a tablet press machine at 20 MPa for5 min and then an effervescent tablet (125 mm id) was ob-tained.

2.3 EADLLME procedure

Effervescent agent (0.696 g) was placed in a 50 mL screw-captube with conic bottom. Then, 120 �L of chlorobenzene (asextraction solvent) was added into the tube. Subsequently,a 10 mL of aqueous sample was added. The effervescenceoccurred from the bottom to top of the tube immediately andthe extraction solvent was homogeneously distributed intothe aqueous sample. The target analytes were extracted intothe fine extraction solvent droplets. When the effervescentreaction finished, the solution was centrifuged for 3 min at3800 rpm and the organic phase was settled at the bottomof the test tube. An amount of 50 �L of sediment phasewas transferred into a 2 mL glass vial by a pipette and, afterevaporation of the solvent under nitrogen stream, the residue


J. Sep. Sci. 2014, 37, 3157–3163 Sample Preparation 3159

was redissolved in 100 �L acetonitrile and injected into theLC system for analysis.

2.4 Chromatographic separation

An Agilent 1100 HPLC system (Agilent Technologies, CA,USA) equipped with a UV-Vis detector was used. The ana-lytes were separated on a ZORBAX Eclipse XDB C18 column(150 × 4.6 mm × 5 �m, Agilent Technologies). The mo-bile phase, which contains acetonitrile (A) and water (B), waspumped at a flow rate of 1.0 mL/min. The gradient elutionstarted with 30% acetonitrile, followed by a linear gradientfrom 0 to 5 min to 45% acetonitrile, then raised to 65% ace-tonitrile from 5 to 20 min, which was followed by a lineargradient of 30% acetonitrile from 20 to 25 min, and thenthe system was reequilibrated at the initial conditions (30%acetonitrile) from 25 to 30 min. The detection wavelengthwas 254 nm. The column temperature was set at 25�C andthe injection volume was 10 �L. The data were collected andprocessed by ChemStation software.

3 Result and discussion

In order to obtain the optimum EADLLME conditions, sev-eral parameters including the composition of effervescentagent, amount of effervescent agent, formulation of effer-vescent agent, adding mode of effervescent agent, type ofextraction solvent, volume of extraction solvent, and effectof pH were investigated. Ten milliliter of aqueous solutionspiked with 0.5 mg/L each analyte (except for kresoxim-methyl that was spiked at 1 mg/L) was used to study theextraction performance under different experimental condi-tions. The experiments were performed by modifying oneparameter at a time while keeping the remaining parametersconstant. Each optimization experiment was replicated threetimes.

3.1 Composition of effervescent agent

An appropriate effervescent agent employed in thisEADLLME procedure should be able to introduce a vigorouseffervescent reaction in aqueous samples in order to assistthe dispersion of extraction solvent rapidly. The effervescentagent contained two main components, namely, a carbondioxide source and proton donor. The appropriate selectionof the two elements has a critical effect on the dispersion ofextraction solvent and transfer of target analytes.

3.1.1 Types of carbon dioxide source and proton

donor

Sodium bicarbonate, sodium carbonate, potassium bicarbon-ate, and potassium carbonate were investigated as carbondioxide sources. Sodium dihydrogen phosphate and citric

acid were examined as proton donors. Eight different kindsof effervescent agents, considering all the possible combi-nations, were prepared maintaining the appropriate ratio onaccount of the stoichiometry of the corresponding chemicalreactions. The amount of effervescent agent was selected toproduce 0.001 mol carbon dioxide in this step.

Some main characteristics of the effervescent agents,such as the effervescent time and pH variation of aqueoussample after effervescent process, were shown in Table 1. Theresults indicated that the effervescent time ranged from 0.8to 18.5 min depending on different compositions of efferves-cent agents, and all the effervescent agents caused negligiblepH variations in aqueous samples. Effervescent time is a keycharacteristic of an effervescent agent. In principle, the influ-ence of the effervescent time on the extraction efficiency iscontradictory, because a faster effervescence involves a morevigorous dispersion of extraction solvent, which may increasethe extraction efficiency but also a lower extraction time,which may decrease the extraction efficiency [17]. The re-sults presented in Supporting Information Fig. S1 show thatthe combination of citric acid and potassium carbonate gavethe best extraction efficiency and the whole effervescent pro-cedure cost only 0.8 min (Table 1). Therefore, citric acid wasselected to be the proton donor and potassium carbonate wasselected to be the carbon dioxide source in the further study.

3.1.2 Ratio between carbon dioxide source and

proton donor

The ratio between carbon dioxide source and proton donoris another parameter that can influence the effervescent re-action and thus the extraction efficiency. Generally, a morevigorous effervescence can be achieved by adding excessivecarbon dioxide source or excessive proton donor. In this work,the molar ratio between citric acid (as proton donor) andpotassium carbonate (as carbon dioxide source) were set tobe 0.67:1 (based on the stoichiometry of the chemical reac-tion), 0.67:1.5 (carbon dioxide source excess), and 1:1 (protondonor excess). The results in Supporting Information Fig. S2show that the best extraction efficiency could be achievedwhen excessive proton donor was present. Thus, the molarratio between citric acid and potassium carbonate were set tobe 1:1 in subsequent experiments.

3.2 Amount of effervescent agent

Generally, adding more effervescent agent into the aqueoussample can produce more carbon dioxide to assist the dis-persion of extraction solvent and promote the transfer of thetarget analytes. However, with the increase of the effervescentagent amount, the ionic strength and viscosity of the solutionincreases, and thereby the extraction efficiency may subse-quently decrease due to the viscous resistance effect [20]. Inthis study, the effervescent agent amount was investigated inthe range of 0.348–1.004 g (to produce the amount of car-bon dioxide in the range of 0.001–0.003 mol). Supporting



Table 1. Main characteristics of the effervescent agents using different compositions

Composition

Proton donor Carbon dioxide source Effervescent time (min) �pH

Sodium dihydrogen phosphate (0.001 mol) Sodium bicarbonate (0.001 mol) 7.5 −0.3Sodium dihydrogen phosphate (0.002 mol) Sodium carbonate (0.001 mol) 18.5 −0.1Sodium dihydrogen phosphate (0.001 mol) Potassium bicarbonate (0.001 mol) 3 −0.2Sodium dihydrogen phosphate (0.002 mol) Potassium carbonate (0.001 mol) 5.5 −0.1Citric acid (0.00033 mol) Sodium bicarbonate (0.001 mol) 1.5 −0.9Citric acid (0.00067 mol) Sodium carbonate (0.001 mol) 4 −0.8Citric acid (0.00033 mol) Potassium bicarbonate (0.001 mol) 0.8 −1.0Citric acid (0.00067 mol) Potassium carbonate (0.001 mol) 0.8 −0.9

Information Fig. S3 shows that the enrichment factors (EFs)of the target analytes increased with the increase of efferves-cent agent amount to 0.696 g and then remained constant.Consequently, the further study was conducted by adding0.696 g effervescent agent.

3.3 Formulation of effervescent agent

Two types of effervescent agent formulation, powder andtablet, were compared. The results in Supporting Informa-tion Fig. S4 showed that the effervescent powder and theeffervescent tablet both gave good extraction performances.Effervescent powder was chosen for further experiments. Ef-fervescent tablet is also selectable especially in mass produc-tion because of its advantage of portability and convenience.

3.4 Adding mode of effervescent agent

In order to obtain a good dispersion performance, the effer-vescence should occur from down to the top of the test tube.In this study, two adding modes of the effervescent agentwere compared (Fig. 1). In mode (A), the effervescent agentwas initially placed at the bottom of the test tube and thenthe extraction solvent and the aqueous sample were added.In mode (B), the aqueous sample was initially placed in thetest tube, and then the extraction solvent and the effervescentagent were added from above into the aqueous sample. Sup-porting Information Fig. S5 shows that a better extractionefficiency could be achieved by mode (A). Therefore, furtherexperiments were performed using mode (A).

3.5 Type and volume of extraction solvent

The selection of an appropriate extraction solvent is an impor-tant parameter of the proposed method. The requirementsas a good extraction solvent are as follows: higher densitythan that of water, low solubility in water, and high extrac-tion capability for the target analytes [21]. Three extractionsolvents, chloroform, carbon tetrachloride, and chloroben-zene, were compared. The average EFs obtained with the dif-ferent extraction solvents (Supporting Information Fig. S6)

showed that chlorobenzene was the optimum extractionsolvent.

The effect of extraction solvent volume on the extrac-tion efficiency was investigated with chlorobenzene rangingfrom 80 to 150 �L. As shown in Supporting InformationFig. S7, all analytes achieved the maximum EFs when 120 �Lof chlorobenzene was used. Thus, 120 �L of chlorobenzenewas chosen for subsequent studies.

3.6 Effect of pH

The pH of the aqueous sample determines the existing formsof target analytes, and thus can affect the transfer of targetanalytes from aqueous phase to organic phase. The effect ofthe aqueous sample pH was studied by adjusting the pH inthe range of 3–9 with HCl and NaOH. The results in Sup-porting Information Fig. S8 indicated that the pH had littleeffect on the extraction efficiency of pyrimethanil, fludioxonil,and cyprodinil in the pH range of 3–9. For kresoxim-methyl,the pH had little effect on the extraction efficiency in the pHrange of 3–7. However, when the pH was adjusted to 9, theanalytical response of kresoxim-methyl decreased apparently.Thus, in the further study, the pH of the aqueous samplesshould be controlled in the range of 3–7. Generally, the pHof the juice samples was in the range of 3–7. Therefore, thepH adjustment is unnecessary for real juice sample analysis.

3.7 Application of the proposed method in apple

juice samples

3.7.1 Analytical performance of EADLLME

The analytical parameters, including linearity and LODs ofthe proposed EADLLME method, were evaluated under theoptimized condition. In order to validate the linearity, theproposed method was applied to a series of aqueous solu-tions containing various concentrations of analytes. The lin-earity was observed in the concentration range from 0.05to 2 mg/L for pyrimethanil, fludioxonil, and cyprodinil, and



Figure 1. Two different adding modesof effervescent agent.

Table 2. Analytical parameters of the proposed EADLLMEmethod

Analyte Linearrange(mg/L)

Linear equation �a) LODb)

(mg/L)

Pyrimethanil 0.05–2 y = 1698.7x + 94.304 0.999 0.005Fludioxonil 0.05–2 y = 1628.8x + 48.865 0.999 0.007Cyprodinil 0.05–2 y = 1297.9x + 0.7876 0.998 0.006Kresoxim-methyl 0.1–4 y = 963.43x + 30.317 0.998 0.01

a) Correlation coefficient.b) Limit of detection.

from 0.1 to 2 mg/L for kresoxim-methyl with the correlationcoefficients (�) >0.998. Each level had three replicates. TheLODs of the method, based on an S/N of 3, ranged between0.005 and 0.01 mg/L for the target analytes. All of the analyt-ical parameters are summarized in Table 2.

3.7.2 Real sample analysis

To evaluate the performance of the proposed EADLLMEmethod in real samples, the determination of the target an-alytes in apple juice samples before and after fortificationat three concentrations were performed under the optimumconditions described above. Each experiment had three repli-cates. The results indicated that no residues of the targetanalytes were found in these real samples. The recoveries of

Table 3. Recoveries and EFs of fungicides from apple juice sam-ples using optimized EADLLME (n = 3)

Analyte ConcentrationSpiked (mg/L)

Extractionrecovery (%)

RSDa)

(%)EF

Pyrimethanil 0.05 109.7 4.1 115.40.5 72.4 1.2 76.21 73.5 3.3 77.3

Fludioxonil 0.05 106.4 5.7 112.00.5 77.7 5.1 81.81 84.7 6.3 89.2

Cyprodinil 0.05 110.8 3.4 116.60.5 89.6 6.3 94.31 86.1 3.8 90.6

Kresoxim-methyl 0.1 109.9 6.4 115.61 91.9 6.8 96.72 93.0 4.3 97.9

a) Relative standard deviation.

the method were expressed as the mean percentage betweenthe amounts found and those added. As shown in Table 3, therecoveries of the proposed method were in the range of 72.4–110.8% with the RSD ranging from 1.2 to 6.8%. SupportingInformation Fig. S9 shows the typical chromatograms of theapple juice samples that were spiked at a concentration of0.05 mg/L for each analyte (except for kresoxim-methyl at aconcentration of 0.1 mg/L) and the blank.



Table 4. Comparison of the proposed EADLLME method with other methods in the determination of selected fungicides in aqueoussamples

Method Target fungicide LODa) (mg/L) Recovery (%) RSDb) (%) Extraction time (min) EFc) Reference

DLLME Cyprodinil, fludioxonil, etc. 0.0003–0.001 81–120 1–14 1 8–86 [28]DLLME-SFO Pyrimethanil, cyprodinil,

kresoxim-methyl, etc.0.005–0.05 72–118 1–14 10 36–56 [29]

UASEME Kresoxim-methyl, etc. 0.002–0.004 83–98 3–6 1 95–135 [30]USAEME Pyrimethanil, cyprodinil,

kresoxim-methyl, etc.0.003–0.02 30–108 4–9 5 100–200 [25]

USAEME Pyrimethanil,kresoxim-methyl etc.

0.001–0.002 88–137 3–10 15 88–137 [31]

EADLLME Pyrimethanil, fludioxonil,cyprodinil, andkresoxim-methyl

0.005–0.01 72–111 1–7 0.8 76–117 This work

DLLME-SFO, dispersive liquid–liquid microextraction based on solidification of floating organic solvent droplets; UASEME, ultrasound-assisted surfactant-enhanced emulsification microextraction.a) Limit of detection.b) Relative standard deviation.c) Enrichment factor.

3.8 Comparison of EADLLME with other

microextraction techniques

The proposed EADLLME method has several advantagesover other microextraction techniques. Compared with SPME[22, 23], single-drop microextraction [24], and ultrasound-assisted dispersive LPME [25, 26], EADLLME substantiallyshortens the extraction time. Compared with the conventionalDLLME [3], no organic disperser solvent is needed in thismethod. Compared with USAEME [4,27] and vortex-assisteddispersive liquid–liquid microextraction [5], no special instru-ment such as ultrasonic cleaning machine or vortex agitatoris needed in this method. Table 4 indicates the values ofLOD, recovery, RSD, EF, and extraction time of the proposedmethod and other methods for the determination of the tar-get fungicides in aqueous samples [25, 28–31]. EADLLME isa simple, rapid, and environmentally friendly method for thedetermination of the target fungicides in juice samples.

4 Concluding remarks

In this study, a novel microextraction technique, EADLLME,has been developed for the extraction and preconcentration offungicides in aqueous samples. Through the use of an effer-vescent agent, the extraction solvent can be homogeneouslydispersed into the aqueous sample, which enhances the mass-transfer of the target analytes. The method is rapid, precise,efficient, and environmentally friendly. In addition, no specialinstrument is required. These advantages make EADLLMEa feasible alternative method to determine pesticide residuesin juice samples.

This work was partly supported by National Science Foun-dation for Fostering Talents in Basic Research of China, Itemnumber: J1210064.

The authors have declared no conflict of interest.

5 References

[1] Arthur, C. L., Pawliszyn, J., Anal. Chem. 1990, 62, 2145–2148.

[2] Jeannot, M. A., Cantwell, F. F., Anal. Chem. 1996, 68,2236–2240.

[3] Rezaee, M., Assadi, Y., Milani Hosseini, M. R., Aghaee,E., Ahmadi, F., Berijani, S., J. Chromatogr. A 2006, 1116,1–9.

[4] Regueiro, J., Llompart, M., Garcia-Jares, C., Garcia-Monteagudo, J. C., Cela, R., J. Chromatogr. A 2008, 1190,27–38.

[5] Yiantzi, E., Psillakis, E., Talanta 2010, 80, 2057–2062.

[6] Farajzadeh, M. A., Mogaddam, M. R. A., Anal. Chim. Acta2012, 728, 31–38.

[7] Hu, J., Wu, X., Feng, Y., J. Chromatogr. A 2010, 1217,7010–7016.

[8] Tsai, W., Huang, S., J. Chromatogr. A 2009, 1216, 5171–5175.

[9] Tseng, W., Chen, P., Huang, S., Talanta 2014, 120, 425–432.

[10] Chen, P., Haung, W., Huang, S., J. Chromatogr. B 2014,955–956, 116–123.

[11] Jia, C., Zhu, X., Wang, J., Zhao, E., J. Chromatogr. A2010, 1217, 5868–5871.

[12] Giokas, D. L., Sakkas, V. A., Albanis, T. A., Lampropoulou,D. A., J. Chromatogr. A 2005, 1077, 19–27.

[13] Zhao, W., Sun, X., Zhou, Z., Food. Chem. 2011, 127, 683–688.

[14] Takagai, Y., Hinze, W. L., Anal. Chem. 2009, 81, 7113–7122.

[15] Lasarte-Aragones, G., Lucena, R., Cardenas, S.,Valcarcel, M., J. Chromatogr. A 2011, 1218, 9128–9134.

[16] Lasarte-Aragones, G., Lucena, R., Cardenas, S.,Valcarcel, M., Anal. Bioanal. Chem. 2013, 405, 3269–3277.



[17] Lasarte-Aragones, G., Lucena, R., Cardenas, S.,Valcarcel, M., Anal. Chim. Acta 2014, 807, 61–66.

[18] Dreassi, E., Zanfini, A., Zizzari, A. T., Rosa, C. L., Botta, M.,Corbini, G., LWT-Food. Sci. Technol. 2010, 43, 1301–1306.

[19] Sagratini, G., Mane, J., Giardina, D., Damiani, P., Pico, Y.,J. Chromatogr. A 2007, 1147, 135–143.

[20] Zacharis, C. K., Christophoridis, C., Fytianos, K., J. Sep.Sci. 2012, 35, 2422–2429.

[21] Leong, M., Fuh, M., Huang, S., J. Chromatogr. A 2014,1335, 2–14.

[22] Rial-Otero, R., Yague-Ruiz, C., Cancho-Grande, B., Simal-Gandara, J., J. Chromatogr. A 2002, 942, 41–52.

[23] Vazquez, P. P., Mughari, A. R., Galera, M. M., J. Sep. Sci.2008, 31, 56–63.

[24] Vinas, P., Martınez-Castillo, N., Campillo, N., Hernandez-Cordoba, M., J. Chromatogr. A 2010, 1217, 6569–6577.

[25] Wang, S., Ren, L., Xu, Y., Liu, F., Microchim. Acta 2011,173, 453–457.

[26] Yan, H., Du, J., Zhang, X., J. Sep. Sci. 2010, 33, 1829–1835.

[27] Jia, C., Zhu, X., Zhao, E., J. Sep. Sci. 2010, 33, 244–250.

[28] Rodrıguez-Cabo, T., Rodrıguez, I., Ramil, M., Cela, R., J.Chromatogr. A 2011, 1218, 6603–6611.

[29] Fan, R., Liu, C., Liu, F., J. AOAC Int. 2014, 97, 183–187.

[30] Liang, P., Liu, G., Wang, F., Wang, W., J. Chromatogr. B2013, 926, 62–67.

[31] Liang, P., Wang, F., Wan, Q., Talanta 2013, 105, 57–62.


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