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Rui Zhang1 Chuanliu Wang2 Qiaohong Yue1 Tiecheng Zhou1 Na Li3 Hanqi Zhang3 Xiaoke Hao1 1 Department

of Clinical Laboratory, Xijing Hospital, Fourth Military Medical University, Xi’ an, China 2 Xi’ an Research Institute of China Coal Technology and Engineering Group Corp, Xi’ an, China 3 College of Chemistry, Jilin University, Changchun, China Received May 25, 2014 Revised August 5, 2014 Accepted August 6, 2014

Research Article

Ionic liquid foam floatation coupled with ionic liquid dispersive liquid–liquid microextraction for the separation and determination of estrogens in water samples by high-performance liquid chromatography with fluorescence detection An ionic liquid foam floatation coupled with ionic liquid dispersive liquid–liquid microextraction method was proposed for the extraction and concentration of 17-␣-estradiol, 17␤-estradiol-benzoate, and quinestrol in environmental water samples by high-performance liquid chromatography with fluorescence detection. 1-Hexyl-3-methylimidazolium tetrafluoroborate was applied as foaming agent in the foam flotation process and dispersive solvent in microextraction. The introduction of the ion-pairing and salting-out agent NH4 PF6 was beneficial to the improvement of recoveries for the hydrophobic ionic liquid phase and analytes. Parameters of the proposed method including concentration of 1-hexyl-3methylimidazolium tetrafluoroborate, flow rate of carrier gas, floatation time, types and concentration of ionic liquids, salt concentration in samples, extraction time, and centrifugation time were evaluated. The recoveries were between 98 and 105% with relative standard deviations lower than 7% for lake water and well water samples. The isolation of the target compounds from the water was found to be efficient, and the enrichment factors ranged from 4445 to 4632. This developing method is free of volatile organic solvents compared with regular extraction. Based on the unique properties of ionic liquids, the application of foam floatation, and dispersive liquid–liquid microextraction was widened. Keywords: Dispersive liquid-liquid microextraction / Estrogens / Fluorescence detection / High-performance liquid chromatography / Ionic liquid foam floatation DOI 10.1002/jssc.201400568

1 Introduction Ionic liquids (ILs) are semiorganic molten salts, which consist of organic cations and various anions with melting points at or below 100⬚C [1]. They have attracted extensive attention because of their advantages. Therefore, ILs are considered as replacements for conventional organic solvents and have found wide application in analytical chemistry, such as extraction solvents in dispersive liquid–liquid microextraction (DLLME) [2, 3], microwave-assisted ionic liquid microextraction [4], aqueous two-phase floatation [5], ionic liquid solvent

Correspondence: Professor Xiaoke Hao, Department of Clinical Laboratory, Xijing Hospital, Fourth Military Medical University, Xi’an, China E-mail: [email protected] Fax: +86-029-82550450

Abbreviations: DLLME, dispersive liquid–liquid microextraction; IL, ionic liquid; ILDLLME, ionic liquid dispersive liquid– liquid microextraction; ILFOF, ionic liquid foam floatation; ILFOF-ILDLLME, ionic liquid foam floatation coupled with ionic liquid dispersive liquid–liquid microextraction  C 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

floatation [6], and single drop microextraction [7]. ILs are not only used as alternative green solvents or synthesis, catalysis, and biocatalysis, but also as electrolytes, or modifiers of mobile and stationary phases in the separation science [8–13]. ILs contain a long n-alkyl substituent chain on cation and they are a novel cationic surfactant [14–16]. DLLME uses microliter volumes of extraction solvent with many advantages [17–20]. The advantages of DLLME are simplicity of operation, rapidness, cost effectiveness, high enrichment capabilities, and environmental benignity. However, volatile organic solvents were still used as the disperser solvent in the DLLME. The volume of the analyzed samples was between 2 and 20 mL for DLLME [21–23], so that it was not appropriate for large amounts of samples. The foam floatation, which is based on the affinity of particles to air bubbles that accumulate on the surface of the bubbles forming a cell-enriched foam [24], is appropriate for large-volume aqueous samples. Since the concentrations of some compounds in water samples are usually at a trace level, the efficient enrichment of them is vital for further analysis. In this work, Colour Online: See the article online to view Fig. 4 in colour. www.jss-journal.com

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the advantages of ILFOF and ILDLLME method was combined and developed for higher enrichment than these two methods separately. The detection of natural and synthetic estrogens in water has attracted great interest in the research community and the general public because of their potential adverse ecological effects [25]. A broad number of natural and synthetic estrogens can be discharged into the aqueous environment via sewage treatment plants [26], which has given rise to decreased sperm counts, increased testicular, prostate, and breast cancer, and to reproductive disorders in humans [27, 28]. The estrogens are frequently detectable in sewage treatment plant effluents and receiving surface waters at concentrations ranging from pg to ng/L [29]. The natural estrogen metabolite estrone could be found at average concentration of 52 pg/L in open-ocean water samples from tropical regions [30], Panter et al. [31] found a significant vitellogenin response to some estrogens at concentrations of 100 and 31.8 ng/L, respectively, in the male fathead minnow. Owing to the low concentrations of steroid pollutants (tens to hundreds of ng/L) in environmental samples, the analyses require highly sensitive methods combined with efficient preseparation and preconcentration techniques. SPE using various sorbent types and elution solvents is one of the most often employed sample pretreatment methods [32–35]. However, this method is time consuming, and relatively large amounts of organic solvent are used. Thus, a simple, green, reliable, sensitive, and cost-effective pretreatment method should be developed. For detection, GC–MS and LC–MS/MS have been used to analyze estrogens in water samples [36, 37]. However, the sample derivatization of GC–MS proved complicated, and the instruments of LC–MS used for this purpose are very expensive [38, 39]. HPLC with fluorescence detection is a fast, simple, easy-to-use, and widely available technique. In this paper, ionic liquid foam floatation coupled with ionic liquid dispersive liquid–liquid microextraction (ILFOFILDLLME) was developed for the extraction and concentration of 17-␤-estradiol-benzoate, 17-␣-estradiol, and quinestrol from water. Several experimental conditions were studied and optimized.

2 Materials and methods 2.1 Chemicals and materials 17-␤-Estradiol-benzoate (purity > 99.0%), 17-␣-estradiol (purity > 99.0%), and quinestrol (purity > 98.5%) were obtained from Sigma (St. Louis, MO, USA), and the chemical structures of the estrogens are shown in Fig. 1. Standard stock solutions for the estrogens at the concentration level of 40 ␮g/mL were prepared in methanol and the working standard solutions at different concentrations were prepared by diluting the stock solutions with methanol. Chromatographic-grade acetonitrile and methanol were obtained from Fisher Scientific (Pittsburgh, PA, USA). Ammonium hexafluorophosphate ([NH4 ][PF6 ]) and the 1-alkyl-3-methylimidazolium ionic liq C 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Figure 1. Chemical structures of the estrogens.

uids, including [C6 MIM][BF4 ], [C4 MIM][PF6 ], [C6 MIM][PF6 ], and [C8 MIM][PF6 ] were purchased from Cheng-jie Chemical (Shanghai, China). Water was purified with a distilling apparatus (Rong-hua, Jiangsu, China) and filtered through a 0.45 ␮m membrane. 2.2 Apparatus Shimadzu HPLC-20AB Class VP HPLC system (Shimadzu Technologies, Kyoto, Japan) equipped with a fluorescence detector was employed. The fluorescence spectra of three estrogens were measured on a Shimadzu RF-5301PC fluorescence spectrophotometer (Kyoto, Japan). The chromatographic separation of the analytes was carried out on a Zorbax Eclipse SB-C18 column (3.5 ␮m, 4.6 mm × 150 mm, Agilent, USA). A high-speed refrigerated centrifuge (Beckman, USA) was employed.

2.3 Sample preparation In this work, environmental water samples, including lake water and well water were collected from Changchun, China for validating the proposed method. The spiked samples containing the analytes were prepared by spiking the working standard solutions into the samples. Then the water samples were filtered through a 0.45 ␮m membrane using a Millipore YT30 142HW device and stored at 4⬚C.

2.4 Determination of target compounds by HPLC The sample injection volume was 4 ␮L, and the temperature of the column was controlled at 40⬚C. The mobile phase consisted of acetonitrile (A) and water (B). The gradient program was as follows: 0–15 min, 45% A. The flow rate of the mobile phase was kept at 0.5 mL/min. The excitation and emission wavelengths for the determination of the three analytes were 265 and 311 nm, respectively. www.jss-journal.com

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Figure 2. The experimental system (1) nitrogen cylinder; (2) flow meter; (3) floatation vessel; (4) foam; (5) sample solution; (6) centrifuge tube; (7) foam solution.

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increased with the increase of alkyl chain length (n) at the 1-position of the cation [19]. Consideration of the microextraction process, [C6 MIM][BF4 ] was chosen as the foaming agent. In this section, the concentration of [C6 MIM][BF4 ] in floatation solution was studied at 3.97, 7.94, 39.7, 79.4, and 158.8 ␮g/mL, and the other experimental conditions were used at their best conditions (Section 2.5). The recoveries obtained at different concentration of [C6 MIM][BF4 ] (3.97, 7.94, 39.7, 79.4, and 158.8 ␮g/mL) showed a rapid decrease from 3.97 to 39.7 ␮g/mL and a slow decrease thereafter. It was observed that when the concentration of [C6 MIM][BF4 ] was lower than 3.97 ␮g/mL, the amount of foam is little. At the concentration of 3.97 ␮g/mL for [C6 MIM][BF4 ] added in the sample solution, the recoveries of three estrogens are highest. The concentration of [C6 MIM][BF4 ] in the floatation solution was chosen at 3.97 ␮g/mL in this work.

2.5 ILFOF-ILDLLME

3.1.2 The flow rate of the carrier gas

An amount of 160 mL of sample solution was transferred to a floatation vessel, and the concentration of [C6 MIM][BF4 ] was 3.97 ␮g/mL. The sample solution was blown-through by a carrier gas at the flow rate of 600 mL/min for 15 min (Fig. 2). The analytes were extracted and transferred from the sample solution to the surface of the solution by the foam of [C6 MIM][BF4 ]. The foam was introduced into a centrifuge tube. An amount of 60 ␮L of [C6 MIM][PF6 ] was put into the tube, 0.3 g NH4 PF6 and 3.0 g NaCl were added also. The suspension was shaken for 10 min. Then the centrifugation was performed at 4⬚C for 15 min at 15 000 rpm, and the IL phase was deposited in the bottom of the centrifuge tube. The IL phase was carefully taken out with the HPLC microsyringe as the analytical solution. An amount of 4 ␮L of IL was injected into the HPLC system and detected under the conditions mentioned above.

N2 was used as carrier gas and the influence of the flow rate of the carrier gas was studied. In this section, the flow rate of carrier gas was investigated at 480, 600, 720, and 840 mL/min, and the other experimental conditions were performed at their best conditions (Section 2.5). The recoveries obtained at different flow rate (480, 600, 720, and 840 mL/min) showed a rapid increase from 480 to 600 mL/min, and the recoveries were almost constant when the volume increased from 600 to 840 mL/min. When the flow rate is low, the recoveries of the estrogens are low. The estrogens were not efficiently taken from the bulk sample solution to its surface. With the increase of the flow rate of the carrier gas, the amount of the foam increased. Floatation efficiency increases with the increase of gas flow rate and more analytes can be transferred into the tube that results in the increase of the recoveries. When the flow rate was high enough, the recoveries of estrogens did not increase remarkably. The flow rate of the carrier gas was chosen as 600 mL/min in this work.

3 Results and discussion The experimental parameters affecting the performances of ILFOF-ILDLLME were studied separately by analyzing spiked water samples. The samples were prepared by spiking standard solutions in pure water and in the samples the concentration of 17-␤-estradiol-benzoate, 17-␣-estradiol, and quinestrol were 0.46, 0.34, and 0.38 ng/mL, respectively.

3.1 Selection of ILFOF-ILDLLME 3.1.1 Concentration of [C6 MIM][BF4 ] in floatation solution It is proved that ILs had foaming ability in aqueous solution no matter whether they were hydrophilic or hydrophobic. ILs can be used as the foaming agents when the concentration of the ILs was in the proper ranges, and their foamability  C 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

3.1.3 Foam floatation time The floatation time is very important for enhancing separation and enrichment efficiency. In this section, the foam floatation time was examined at 5, 10, 15, 20, and 25 min, and the other experimental conditions were performed at their best conditions (Section 2.5). The recoveries obtained at different floatation time (5, 10, 15, 20, and 25 min) showed a rapid increase from 5 to 15 min, and the recoveries slightly change from 15 to 25 min. Three estrogens in the sample solution could not be taken out completely when the floatation time was too short. The results indicate that recoveries of estrogens are unchanged when the floatation time is longer than 15 min. Thus, 15 min was chosen as the floatation time. 3.1.4 pH value of floatation solution It was found that the foamability of the ILs was improved when the sample solution was in the alkaline and acidic www.jss-journal.com

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condition. In this section, the pH value of the sample solution was tested at 2, 4, 6, 8, 10, and 12, and the other experimental conditions were performed at their best conditions (Section 2.5). When the pH value was 2, 4, 6, 8, 10, 12, the volume of the foam was 114, 69, 22, 72, 108, and 130 mL, respectively. The volume of the analyzed samples between 2 and 20 mL was appropriate for DLLME, so the pH value of the sample solution was chosen as 6.0 in this experiment. 3.1.5 Concentration of salt in floatation solution The concentration of salt in floatation solution is an important factor. It was founded that the foamability of IL was enhanced remarkably with the increase of concentration of NaCl ranging from 0 to 12 mg/mL. In this section, the concentration of NaCl in floatation solution was studied at 0, 2, 4, 6, 8, 10, and 12 mg/mL, and the other experimental conditions were performed at their best condition as Section 2.5 mentioned. When the concentration of NaCl was 0, 2, 4, 6, 8, 10, 12 mg/mL, the volume of the foam was 22, 59, 76, 99, 110, 123, and 135 mL, respectively. The volume of the analyzed samples between 2 and 20 mL was appropriate for DLLME, so the concentration of salt in floatation solution was chosen as 0 in this experiment. 3.1.6 Microextraction solvent in ILDLLME In the ILDLLME process, it is very important to select an appropriate extraction solvent. The solvent should have good chromatographic behavior under the selected HPLC conditions, higher density than water, high capability to extract the interesting analytes and low solubility in water. In order to achieve good extraction efficiency of the target compound, the effects of types and volume of the extraction solvent were studied. In this study, [C4 MIM][PF6 ], [C6 MIM][PF6 ], and [C8 MIM][PF6 ] was used as microextraction solvents, and the other experimental conditions were performed at their best conditions (Section 2.5). The solubilities of three ILs in water are 18.8, 7.5, and 2.0 g/L, and the viscosities are 450, 585, and 710 mPa s at 25⬚C, respectively [40]. It was observed that when [C4 MIM][PF6 ] was used as the extraction solvent, the sample solution was always transparent and no IL phase appeared at the bottom of the tube after centrifugation. The reason may be that the solubility of [C4 MIM][PF6 ] in water is higher than those of [C6 MIM][PF6 ] and [C8 MIM][PF6 ]. The recoveries of 17-␤-estradiol-benzoate, 17-␣-estradiol, and quinestrol were 100.0, 101.3, and 97.2% for [C6 MIM][PF6 ], respectively, and 78.3, 83.3, 80.3% for [C8 MIM][PF6 ], respectively. The extraction recoveries obtained with [C6 MIM][PF6 ] were higher than that obtained with [C8 MIM][PF6 ]. And there were serious residues in the HPLC equipment for its high viscosity when [C8 MIM][PF6 ] was used as the microextraction solvent. Therefore, [C6 MIM][PF6 ] was selected as microextraction solvent in this work. In order to evaluate the influence of extraction solvent volume on extraction efficiency, sample solutions containing different volumes of [C6 MIM][PF6 ] were subjected

 C 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

to the same DLLME procedure. The volume of sedimented phase was 10, 22, 35, 50, 60, and 90 ␮L when the volume of extraction solvent was 40, 50, 60, 80, 100, and 150 ␮L, respectively. Figure 3(A) and (B) showed the effect of volume of [C6 MIM][PF6 ] on the extraction recoveries and enrichment factors, respectively. The results indicated that the extraction recoveries for the analytes increase with increasing the volume of [C6 MIM][PF6 ]. However, from Fig. 3(B), it also can be seen that enrichment factors decrease with increasing the volume of [C6 MIM][PF6 ], because the volume of sedimented phase increases. A volume of 60 ␮L was the best compromise between recovery and enrichment and selected in the further experiments. 3.1.7 Salt concentration in ILDLLME sample solution In the extraction, solubility of target analytes in the aqueous phase will be decreased and their partitioning in the extraction phase will be enhanced at the same time [41]. Generally NaCl was used to adjust the ionic strength. In this study, the amount of NaCl was added at 0, 1, 2, 3, and 3.5 g, and the other experimental conditions were performed at their best conditions (Section 2.5). The effect of the concentration of NaCl on the recoveries of target analytes was investigated when the other experimental conditions were constant. The results shown in Fig. 4(A) indicated that the recoveries increased with the increase of NaCl concentration, reach maximum at NaCl concentration of 3.0 g and then unchanged. The salt out effect was enhanced with the increase of the salt concentration. However, when the salt concentration was too high, ion exchange between [PF6 ]− in [C6 MIM][PF6 ] and Cl− in solution occurred and the resulting [C6 MIM]Cl is soluble in water. This process may lead to the decrease of the amount of settled IL phase and the poor extraction performance [42–44]. Considering there is residual cation ([C6 MIM]+ ) in aqueous phase, the ion-pairing agent PF6 – can deposit the residual cation. NH4 PF6 was applied to improve this problem in this work. In this study, the amount of NH4 PF6 was investigated at 0, 0.15, 0.3, 0.45, and 1.0 g, and the other experimental conditions were performed at their best conditions (Section 2.5). The effect of NH4 PF6 was investigated in the range of 0– 1.0 g and the results are shown in Fig. 4(B). The extraction recoveries increased with the increase of amount of NH4 PF6 from 0 to 0.3g, and then unchanged when the amount of NH4 PF6 is higher than 0.3 g. [PF6 ]– is beneficial to the formation of [C6 MIM][PF6 ] and the amount of sedimentary IL phase increases. Meanwhile, the addition of salt can promote the phase separation successfully. Therefore, the content of NH4 PF6 selected was 0.3 g. 3.1.8 Extraction time In this study, the extraction time was investigated at 0, 5, 10, 15, and 20 min, and the other experimental conditions were performed at their best conditions (Section 2.5). Theoretically, the increase of extraction time was beneficial to the

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Figure 3. (A) Effect of the volume of [C6 MIM][PF6 ] on the recoveries of estrogens. (B) Effect of the volume of [C6 MIM][PF6 ] on the enrichment factor of estrogens.

partition equilibrium of target analytes in [C6 MIM][PF6 ]/water system and the improvement of the extraction yields of analytes. When the recoveries obtained at different extraction time (0, 5, 10, 15, and 20 min), the recoveries of the target analytes increase gradually with the increase of the extraction time from 1 to 10 min. The extraction time longer than 15 min resulted in a negligible increase of the recoveries and the equilibrium seemed to be reached. Based on the experimental results, the extraction time was selected to be 15 min.  C 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

3.1.9 Centrifuging time The centrifuging time is very important to ensure an efficient extraction and effect of this variable was examined. The centrifugation was performed at 4⬚C for 5, 10, 15, 20, and 25 min, and the other experimental conditions were performed at their best condition as Section 2.5 mentioned. To achieve a good separation result, the effect of centrifuging time (5, 10, 15, 20, and 25 min) was examined. To reduce the solubility of the resulting IL phase, centrifugation was www.jss-journal.com

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Figure 4. (A) Effect of the amount of NaCl on the recoveries of estrogens. (B) Effect of the amount of NH4 PF6 on the recoveries of estrogens.

performed at 4⬚C, and the centrifugation force was 19 621 × g. The recoveries showed a rapid increase from 0 to 15 min, and the recoveries were almost constant when the centrifuging time increased from 15 to 25 min. The experimental results indicated that the volume of the resulting ionic liquid phase could reach to the maximum value when the centrifuging time was 15 min.

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3.1.10 pH in ILDLLME sample solution The pH of the microextraction solution was studied at 2, 4, 6, 8, 10, and 12, and the other experimental conditions were performed at their best condition as Section 2.5 mentioned. The effect of pH upon the extraction of the analytes from the ILDLLME sample solution was studied at pH 2, 4, 6, 8, 10, 12.

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Figure 5. Chromatograms of sample solution.

Table 1. Standard curves, LOD, and LOQ for steroid hormones

Steroid hormone

Working curves

Correlation coefficient

Concentration range (ng/mL)

LOD (ng/mL)

LOQ (ng/mL)

17-␤-Estradiol-benzoate 17-␣-Estradiol Quinestrol

A = 718684.00 + 3.77 × 106 c A = 103947.26 + 2.77 × 106 c A = 14911.61 + 2.86 × 106 c

0.9988 0.9997 0.9998

0.19  1.45 0.17  1.10 0.17  1.20

0.05 0.05 0.05

0.17 0.17 0.17

A, the peak area; c, concentration of analytes (␮g/mL).

Each operational desired pH value was obtained by the addition of diluted HCl and/or NaOH. The recoveries increased with the increase of the pH value, reached maximum at pH 8 and then decreased. The pKa for 17-␤-estradiol-benzoate, 17-␣-estradiol and quinestrol was 15.06, 10.08, and 13.10, respectively. All the three analytes can be ionized at too high pH values, which can affect the recoveries and stability of the analytes. Therefore, pH 8 was selected for further studies.

3.2 Evaluation of the method The target compounds were identified by their retention time in the chromatograms in comparison to that of the authentic standard analytes. Typical chromatograms of lake water are shown in Fig. 5. The retention time was 8.61 min for 17-␤-estradiol-benzoate, 9.86 min for 17-␣-estradiol, and 10.90 min for Quinestrol. 3.2.1 Working curve and detection limit Under the above mentioned optimal experimental conditions, a series of experiments were performed for obtaining linear range, precision, and detection limit. The results are shown in Table 1. The selected estrogens exhibit good linearity with correlation coefficient (r) of 0.9988–0.9998. The LODs  C 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

and LOQs indicated in Table 1 are determined as the lowest concentration yielding an S/N of 3 and 10, respectively. The concentrations of the target analytes in the extract are higher than the LOQs and lower than upper limits of determination for the proposed method. So the LOQs and linear equations are appropriate to the goal of the proposed method. 3.2.2 Comparison with other methods Extraction and determination of estrogens in water sample by the proposed method was compared with SPE–HPLC [45], dispersive liquid–liquid microextraction micellar electrokinetic chromatography coupled to MS (DLLME–MEKC–MS) [46] and dispersive liquid–liquid microextraction with solidification of a floating organic drop with HPLC (DLLME–SFO– HPLC) [47], and the results are shown in Table 3. As shown in Table 3, the present technique has a great advantage over other similar methods and SPE method in the expenditure of the enrichment factor and organic solvent. Considering the LODs and consumption of organic solvent, the ILFOFILDLLME method should be interesting. 3.2.3 Analysis of samples The practical performance of the present method was validated with two real water samples. No steroid residues at www.jss-journal.com

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Table 2. Analytical results of water samples

Sample

Steroid hormones

Spiked (ng/mL)

Recoveries (%)

Intraday (RSD%, n = 5)

Interday (RSD%, n = 5)

Lake water

17-␤-Estradiol-benzoate

0.23 0.46 0.92 0.17 0.34 0.68 0.19 0.38 0.76 0.23 0.46 0.92 0.17 0.34 0.68 0.19 0.38 0.76

100 99 98 102 104 105 100 100 103 98 98 98 100 100 101 98 99 100

5 4 4 5 5 5 6 5 5 6 6 5 6 5 5 5 5 4

6 5 4 7 6 6 6 6 6 6 6 6 6 5 4 7 6 5

17-␣-Estradiol

Quinestrol

Well water

17-␤-Estradiol-benzoate

17-␣-Estradiol

Quinestrol

Table 3. Comparison of different methods

Method

Enrichment factor

Organic extraction solvent volume(mL)

LOD (ng/mL)

SPE–HPLC DLLME–MEKC– MS DLLME-SFO–HPLC ILFF-ILDLLME

200 100

20.2 0.5

70–610 0.04–1.1

croextraction solvent in the decrease detection limits. No organic solvent was employed in this work. High enrichment factors and acceptable recoveries were achieved. Thanks for the ILFOF, ILDLL hydrophobic ionic liquid microextraction. Fluorescence detection was employed with HPLC to avoid ILs interference peak in the chromatogram, increase sensitivity, and could be applied to the large amounts of aqueous samples.

500 4445–4633

0.2 None

0.8–3.1 0.05

This work was supported by the National Natural Science Foundation of China (No. 81401744). The authors have declared no conflict of interest.

detectable level were found in these samples. The precision and accuracy of the proposed method were evaluated by analyzing these two samples spiked with the estrogens at low, middle, and high concentrations, respectively. The accuracy of the method was determined by calculating recoveries and the precision was determined by calculating the RSDs. The recoveries for three estrogens in water samples are listed in Table 2. The results indicate that the proposed method provides good recoveries (98–105%) and acceptable precisions (7%) and can be applied to the determination of steroid residues in environmental water samples.

4 Conclusion The ILFOF-ILDLLME method was established for the extraction and concentration of 17-␣-estradiol, 17-␤-estradiolbenzoate, and quinestrol in water. In this method, different properties of ILs had been combined and developed. NH4 PF6 was applied to reduce the adding amount of mi C 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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[8] Papageorgiou, N., Athanassov, Y., Armand, M., Bonhote, P., Pettersson, H., Azam, A., J. Electrochem. Soc. 1996, 143, 3099–3108. [9] Armstrong, D. W., He, L., Liu, Y. S., Anal. Chem. 1999, 71, 3873–3876. [10] Huddleston, J. G., Visser, A. G., Reichert, W. M., Willauer, H. D., Broker, G. A., Rogers, R. D., Green Chem. 2001, 3, 156–164. [11] Majewski, P., Pernak, A., Grzymisławski, M., Iwanik, K., Pernak, J., Acta Histochem. 2003, 105, 135–142. [12] Liu, X., Zhou, F., Liang, Y., Liu, W., Tribol. Lett. 2006, 23, 191–196. [13] Ren, R. B., Wang, Y., Zhang, R., Zhang, H. Q., Yu, A. M., Talanta 2011, 83, 1392–1400. [14] Patra, D., Barakat, C., Spectrochim. Acta A 2011, 79, 1823–1828. [15] Behera, K., Pandey, S., J. Phys. Chem. B 2007, 111, 13307–13315. [16] Zhang, R., Li, N., Wang, C. L., Bai, Y. P., Ren, R. B., Gao, S. Q., Yu, W. Z., Zhao, T. Q., Zhang, H. Q., Anal. Chim. Acta 2011, 704, 98–109.

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Ionic liquid foam floatation coupled with ionic liquid dispersive liquid-liquid microextraction for the separation and determination of estrogens in water samples by high-performance liquid chromatography with fluorescence detection.

An ionic liquid foam floatation coupled with ionic liquid dispersive liquid-liquid microextraction method was proposed for the extraction and concentr...
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