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J. Sep. Sci. 2014, 00, 1–6

Xiao Yang1 Chun-Peng Diao2 Ai-Ling Sun1 Ren-Min Liu1 1 School

of Chemistry and Chemical Engineering, Liaocheng University, Liaocheng, China 2 School of Environment and Planning, Liaocheng University, Liaocheng, China Received May 26, 2014 Revised July 9, 2014 Accepted July 11, 2014

Short Communication

Rapid pretreatment and determination of bisphenol A in water samples based on vortex-assisted liquid–liquid microextraction followed by high-performance liquid chromatography with fluorescence detection A method for the rapid pretreatment and determination of bisphenol A in water samples based on vortex-assisted liquid–liquid microextraction followed by high-performance liquid chromatography with fluorescence detection was proposed in this paper. A simple apparatus consisting of a test tube and a cut-glass dropper was designed and applied to collect the floating extraction drop in liquid–liquid microextraction when low-density organic solvent was used as the extraction solvent. Solidification and melting steps that were tedious but necessary once the low-density organic solvent used as extraction solvent could be avoided by using this apparatus. Bisphenol A was selected as model pollutant and vortex-assisted liquid–liquid microextraction was employed to investigate the usefulness of the apparatus. High-performance liquid chromatography with fluorescence detection was selected as the analytical tool for the detection of bisphenol A. The linear dynamic range was from 0.10 to 100 ␮g/L for bisphenol A, with good squared regression coefficient (r2 = 0.9990). The relative standard deviation (n = 7) was 4.7% and the limit of detection was 0.02 ␮g/L. The proposed method had been applied to the determination of bisphenol A in natural water samples and was shown to be economical, fast, and convenient. Keywords: Bisphenol A / High-performance liquid chromatography / Vortexassisted liquid–liquid microextraction / Water samples DOI 10.1002/jssc.201400577

1 Introduction Bisphenol A (BPA), 2,2-bis(4-hydroxyphenyl)propane, has extensively been used in the production of polycarbonate plastics and epoxy resins. Krishnan et al. [1] reported that BPA could be released from polycarbonate flasks during autoclaving and exhibited estrogenic activity, and trace amount of BPA in sea water from Malaga (Spain) and spring water from the fertile plain of Granada (Spain) had been detected by del Olmo et al. [2]. Unfortunately, BPA is a well-known endocrine disrupting chemical and it could cause reproductive abnormalities in various wildlife species. Hence, with the development of water pollution, it is important to establish a simple, efficient, and sensitive method for the determination of BPA in water.

Correspondence: Professor Ren-Min Liu, School of Chemistry and Chemical Engineering, Liaocheng University, Liaocheng 252000, China E-mail: [email protected] Fax: +86-6358-239069

Abbreviations: BPA, bisphenol A; DLLME, dispersive liquid– liquid microextraction; LLME, liquid–liquid microextraction; SFO, solidification of floating organic droplet; VALLME, vortex-assisted liquid–liquid microextraction  C 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Some methods have been reported for the detection of BPA in environmental water and many sample preparation techniques such as LLE [3], SPE [4–9], and molecularly imprinted SPE [10, 11] have been developed for the determination of BPA. Among these methods, LLE requires large volumes of organic solvents and additional concentration steps are necessary. SPE or molecularly imprinted SPE requires small volumes of organic solvent, but the manual version is tedious and time consuming. Analytical microextraction represents an important development in the field of sample preparation, addressing issues of simplicity, miniaturization, and time efficiency [12]. Rezaee et al. [13] introduced an important microextraction technique called dispersive liquid– liquid microextraction (DLLME) for the pretreatment of contaminants in water samples. DLLME is a successful extraction technique, which uses high-density organic solvent as the extraction solvent and polar solvent (water miscible) as the dispersive agent for the purpose of making the extraction solvent fully dispersed into the water. In the process of dispersion, the dispersive solvent carrying extraction solvent disperses in water quickly. After centrifugation of the solution, the extraction solvent precipitates at the bottom of the extraction vessel and analytes are extracted into the extraction Colour Online: See the article online to view Fig. 1 in colour. www.jss-journal.com

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solvent simultaneously. Because of its many advantages such as high enrichment factor and short extraction time, DLLME has been widely used in pesticide residue analysis [14–17]. However, the high-density extraction solvents used in DLLME are normally chlorinated and highly toxic, which restricted the application of DLLME. Some researchers have made great efforts to use low-density solvents as the extraction solvent in DLLME. Khalili-Zanjani et al. [18] reported a novel liquid–liquid microextraction based on solidification of floating organic droplet (LLME-SFO). LLME-SFO is simple and of high accuracy, high precision, low cost, and has minimal organic solvent consumption. Leong and Huang [19] introduced DLLME with solidification of floating organic droplet (DLLME-SFO) on the basis of DLLME and LLME-SFO. The large contact surface between the sample and droplets of the extraction solvent could speed up the mass transfer in DLLME-SFO significantly. Further, vortex-assisted liquid–liquid microextraction (VALLME) was proposed to avoid using dispersive solvent and obtain lower LOD. Similar to the DLLME procedure, a high-density solvent, such as chloroform [20, 21] and ionic liquid [22], could be exploited as the extraction solvent for pretreatment of pollutants in water samples. Low-density organic solvents were also employed as extraction solvents according to the requirement [23,24]. Some researchers reported the application of VALLME for determination of contaminants in various samples such as fruits [25], liquor [26], beverages [27], and sediment [28]. Moreover, the combinations of VALLME and other pretreatment techniques were reported to achieve better performance [29]. Rom´an even reported the application of VALLME for rapid determination of partition coefficient of six compounds (hydroquinone, dichlorvos, simazine, 2,6dichlorophenol, 2,4-dichlorophenol, and naphthalene) in octanol/water [30]. Nonetheless, solidification–melt steps were necessary in these microextraction procedures, which were troublesome and intractable and obstructed the improvement of the efficiency of sample pretreatment. In the present study, VALLME was chosen to speed up the extraction, and a simple apparatus consisting of a cut-glass dropper and a test tube that matched together closely was used to collect the low-density extraction solvent. Solidification–melt steps necessary in VALLME and DLLMESFO were avoided. BPA in water samples was extracted by the proposed method and then determined by HPLC with fluorescence detection.

2 Materials and methods 2.1 Reagent and materials BPA with purity >99% was purchased from Aladdin (Shanghai China). 2-Ethylhexanol, n-hexane, ether, cyclohexane used were of analytical reagent grade (Tianjin Kemiou Chemical Reagent, Tianjin, China). Sodium hydroxide, hydrochloric acid, and sodium chloride used were of analytical grade (Tianjin Fengchuan Chemical Reagent Science & Technol C 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

ogy, Tianjin, China). Acetonitrile and methanol for HPLC analysis were of HPLC grade (Sigma–Aldrich, St. Louis, MO, USA). High-quality water was made in our own laboratory. The stock solution containing 1 mg/L BPA was prepared by dissolving suitable amounts of BPA in methanol and stored at 4⬚C in the dark. The water samples taken from The Beijing–Hangzhou Grand Canal and Tuhai River in Liaocheng, China, were filtered through a 0.45 ␮m pore size filter membrane prior to analysis. 2.2 The apparatus for VALLME A cut-glass dropper and test tube were matched closely to form an apparatus for the collection of extraction solvent. The outer diameter of the coarse end of the glass dropper was a little smaller than the inner diameter of the test tube in which the extraction procedure was conducted. The vortex mixer was used to speed up the extraction (Shanghai Qingpu Huxi Instrument Factory, Shanghai, China). The whole diagram is shown in Fig. 1. 2.3 HPLC analysis The HPLC analysis procedure was carried out by using an Agilent 1100 HPLC system equipped with a fluorescence detector (Agilent Technologies, Waldbronn, Germany). The excitation wavelength of the fluorescence detector was 283 nm, and the emission wavelength was 323 nm. A Spherigel C18 column (250 × 4.6 mm, 5 ␮m) was employed for HPLC separation and a binary solvent of acetonitrile/water was used as the mobile phase. Acetonitrile in the mobile phase was changed from 50 to 70% in 15 min. The flow rate of the mobile phase was 1.0 mL/min. 2.4 VALLME procedure The schematic procedure of VALLME was shown in (Fig. 1). A 5 mL aqueous solution with 10 ␮g/L of BPA was placed in the test tube and precise quantification of 2-ethylhexanol was added as the extraction solvent. The mixture was shaken vigorously using a vortex mixer for a short time. The coarse end of the glass dropper was then gently put into the sample tube to elevate the level of the sample solution up to the tip of the glass dropper. The fine drops of the extraction solvent gathered to bigger drops and increased the height of the extraction solvent in the small tip of the glass dropper, which was readily available for collection. Then 10 ␮L of 2-ethylhexanol was collected with a microsyringe for HPLC analysis. All experiments were run at least in duplicate during optimization.

3 Results and discussion In order to obtain high extraction efficiency, the effects of various factors, including the type of the extraction solvent, the www.jss-journal.com

Sample Preparation

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Figure 1. The combining apparatus and schematic procedure of VALLME. (I) Extraction solvent was added into the sample solution. (II) With the help of vortex, the sample solution was emulsified and the extraction process was ongoing. (III) Glass dropper coarse (slightly smaller than the diameter of the tube) was inserted into the test tube, extraction solvent formed an upper layer in the tip of the glass dropper after standing for several minutes. (IV) The extraction solvent was collected easily by a microsyringe. (1) microsyringe, (2) cutglass dropper, (3) extraction solvent, (4) 5 mL test tube, (5) sample solution, (6) a plug, (7) vortex mixer.

volume of the extraction solvent, vortex extraction time, the pH, and the concentration of the salt in extracting solutions were all investigated systematically.

3.1 Extraction solvent It is very important to choose a suitable extraction solvent in VALLME. The extraction solvent suitable for VALLME should at least meet some requirements, such as the density of the extraction solvent should be lower than that of water, the solubility of the extraction solvent in water should be low enough, the partition coefficients of the target compound between the extraction solvent and water should be high enough, and the chromatographic peak of extraction solvent and the target compound should be independent. On the basis of these conditions, four kinds of organic solvents including 2-ethylhexanol, n-hexane, ether, and cyclohexane were investigated. The results indicated that 2-ethylhexanol achieved the best extraction efficiency, and the chromatographic peaks of 2-ethylhexanol and BPA were independent (Fig. 2). Therefore, 2-ethylhexanol was chosen as the extraction solvent in the following experiments.

3.2 Volume of extraction solvent In order to investigate the effect of volume of extraction solvent, different volumes of 2-ethylhexanol were tested. It was difficult to collect the extraction solvent after swirling once the volume of extraction solvent was

Rapid pretreatment and determination of bisphenol A in water samples based on vortex-assisted liquid-liquid microextraction followed by high-performance liquid chromatography with fluorescence detection.

A method for the rapid pretreatment and determination of bisphenol A in water samples based on vortex-assisted liquid-liquid microextraction followed ...
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