Hongli Sun, Feng Jiang, Lin Chen, Jing Zheng, Yiwei Wu* and Meilin Liu

Transcription

1 Journal of Chromatographic Science 2014;52: doi: /chromsci/bmt078 Advance Access publication June 21, 2013 Article Determination of Three Phthalate Esters in Environmental Samples by Coal Cinder Extraction and Cyclodextrin Modified Micellar Electrokinetic Chromatography Hongli Sun, Feng Jiang, Lin Chen, Jing Zheng, Yiwei Wu* and Meilin Liu Department of Chemistry and Environmental Engineering, Hubei Key Laboratory of Pollutant Analysis and Reuse Technique, Hubei Normal University, Huangshi, P.R. China *Author to whom correspondence should be addressed. Received 26 July 2012; revised 1 May 2013 A new micellar electrokinetic chromatography (MEKC) method using beta-cyclodextrin (ß-CD) as the electrophoresis additive has been developed for the simultaneous determination of dimethyl phthalate (DMP), diethyl phthalate (DEP) and di(2-ethylhexyl) phthalate (DEHP) in environmental samples. To improve the sensitivity of cyclodextrinmodified MEKC (CD-MEKC), a flow injection procedure using a microcolumn packed with coal cinder as the solid-phase extractant was also investigated for the preconcentration and separation of DMP, DEP and DEHP in environmental samples. Parameters affecting CD- MEKC separation and coal cinder flow injection solid-phase extraction were systematically researched. In the presence of the running buffer [5 mmol/l of borax, 5% (v/v) methanol and 25 mmol/l of sodium dodecyl sulfate at ph 9.5], the addition of 14 mmol/l ß-CD greatly improved the separation efficiency. The analytes were quantitatively adsorbed by coal cinders and readily desorbed quantitatively with 0.2 ml of 10% (v/v) methanol 10 mmol/l disodium hydrogen phosphate. Under the optimum conditions, the enrichment factor of coal cinder was 60, and the determination limits of DMP, DEP and DEHP were 3.07, 2.07 and 4.06 ng/ml, respectively. The presented procedure was successfully applied to determine DMP, DEP and DEHP in landfill leachate and water samples with satisfactory results. Introduction Phthalate esters (PEs) are widely used as plasticizers to soften and increase the flexibility in polyvinyl chloride plastics (PVC) (1), or as non-plasticizers in products such as lubricating oils, automobile parts, paints, glues, insect repellents, photographic films, perfumes and food packaging materials (2). The most common PE is di(2-ethylhexyl)phthalate (DEHP); approximately 95% of DEHP production is directed towards plasticizer use, particularly in PVC products. Recently, the use of other phthalate plasticizers has increased; in particular, diisononyl phthalate (DINP) and diisodecyl phthalate (DIDP) may be more environmentally persistent (3). The toxicological evaluation of these chemicals has shown that some PEs and their metabolic products are reproductive and developmental toxicants in animals and suspected endocrine disruptors in humans (4 6). As a result of their extensive use, manufacture and disposal, living organisms and the entire environment of the earth have been contaminated with PEs (7, 8). Spread through the food chain, they enter the human body directly or indirectly through different pathways of environmental exposure (3 9). Therefore, the need has grown for the accurate determination of trace quantities of PEs in environment samples because of deleterious side effects on human health (10 20). Many analytical techniques, including high-performance liquid chromatography (HPLC) (10 12), gas chromatography (GC) (13 17) and micellar electrokinetic chromatography (MEKC) (18 20), have widely been used to detect PEs in environmental samples. Among these techniques, capillary electrophoresis (CE) has attracted great attention in many application fields for its high separation efficiency, small requirements of sample volume, low reagent consumption and high speed of analysis (21). Nevertheless, despite its advantages, the low concentration sensitivity (because of a short optical path length) and a small injection volume (several nanoliters) make it difficult to meet the requirements for trace analysis in real samples. Therefore, a sample pretreatment procedure, such as cloud point extraction (22), liquid-phase microextraction (23), solidphase extraction (SPE) (24, 25), or solid-phase microextraction (26) usually has to be conducted before analysis. In recent years, SPE has played a prominent role in sample pretreatment. It is generally employed to extract a broad range of chemicals due to its low consumption of organic solvents, simplicity, high recovery and high preconcentration factors (27). He et al. (28) used molecularly imprinted fibers as a solid-phase extractant for the selective extraction of phthalates in an aqueous sample. Asadollahzadeh et al. (29) deposited a carbon nanotube/polypyrrole composite on a stainless steel fiber to extract PEs from aqueous media. Barium alginate caged Fe3O4@C18 magnetic nanoparticles were applied to preconcentrate polycyclic aromatic hydrocarbons and PEs from environmental water samples by Zhang et al. (30). Coal cinder is a solid waste resulting from the coal burning process in all kinds of industrial and private boilers and furnaces. Yang et al. (31) used coal cinders for the removal of phosphorous and other pollutants. Wu et al. (32) also employed coal cinders to isolate para-, meta- and ortho-phenylenediamine isomers from hair dyes. These studies reveal that coal cinders may be used as an inexpensive and satisfactory adsorption medium for the extraction of PEs. Thus far, there have been no reports of coal cinder as adsorbent for extraction of PEs. This paper aims to explore the possibility of using coal cinder as the adsorbent for the extraction of three PEs and betacyclodextrin (ß-CD) as the electrophoresis additive in MEKC, to develop a new method for the simultaneous determination of three PEs from environmental samples by MEKC coupled with SPE. This is the first work in which b-cd is used as an additive to the micelle for the separation of PEs. Factors affecting coal cinder extraction and MEKC separation of three PEs were # The Author [2013]. Published by Oxford University Press. All rights reserved. For Permissions, please journals.permissions@oup.com

2 investigated in detail. The proposed method was applied to the determination of three PEs in environmental samples. Experimental Chemicals and reagents Stock solutions (10.0 mg/ml) of dimethyl phthalate (DMP), diethyl phthalate (DEP) and DEHP were prepared with chromatographic purity (Boyun Reagent, Shanghai, China). Analytical standard mixture solutions of PEs were prepared by mixing and diluting the individual stock solutions with doubly distilled water (DDW). ß-CD of analytical purity was purchased from Tianjin Kermel Chemical Reagents Development Center (Tianjin, China). The coal cinder of mesh size (obtained from the boiler house of Hubei Normal University) was immersed in 3.0 mol/l hydrogen chloride (HCl) and sodium hydroxide (NaOH), each for 24 h, filtered, washed with DDW until it became neutral and dried prior to storage for later use. The results of Brunauer Emmett Teller (BET) measurements and the curve of nitrogen desorption (32) showed that the specific surface area of the coal cinder was 50.3 m 2 /g 21, and the pore size distribution (PSD) curve for the coal cinder was narrow (approximately 2 4 nm). The running buffer was 5 mmol/l of borax, 5% (v/v) of methanol, 14 mmol/l of ß-CD and 25 mmol/l of sodium dodecyl sulfate (SDS) at ph 9.5. Other chemicals were of analytical reagent grade and obtained from Shanghai Chemical Reagent Corporation (Shanghai, China). All solutions were prepared by using DDW, stored at 48C in a refrigerator and filtered through a 0.45 mm membrane before use. Instrumentation A CE instrument (Beijing Cailu Scientific Instrument, China), equipped with an ultraviolet (UV) detector for absorbance measurements, was used for MEKC. A 51 cm uncoated fused-silica capillary (50 mm i.d. 375 mm o.d.) was used (Yongnian Optical Fiber, Hebei, China) with an effective length of 43 cm. The CE system was interfaced with a microcomputer. Scanning electron micrography (SEM) of coal cinders was performed with an S-3400N scanning electron microscope (Hitachi, Tokyo, Japan). A home-made polytetrafluoroethylene (PTFE) microcolumn ( mm i.d.) was used in the extraction and a minimum length of PTFE tubing (0.5 mm i.d.) was used for flow injection (FI). An HL-2 peristaltic pump (Shanghai Qingpu Instrument Factory, China) was used to control the flow rate of the microcolumn. The reported ph of the solution was carefully measured with a PHS-3C ph meter (Shanghai Precision & Scientific Instrumental, Shanghai, China). Experiment procedure SPE column preparation A total of 90.0 mg of coal cinders was filled into a PTFE microcolumn ( mm i.d.), which was plugged with a small portion of skimmed cotton at both ends. The column was conditioned with DDW. MEKC preparation All new capillaries were rinsed sequentially with ethanol, 1.0 mol/l HCl, 1.0 mol/l NaOH and DDW for 30 min and equilibrated with the running buffer for 20 min. To achieve reproducibility of migration times and to avoid solute adsorption, the capillary was washed between analyses with ethanol for 1 min and DDW for 2 min, and finally equilibrated with the running buffer for 5 min. Samples were pressure-injected at the anodic side at 0.5 psi (1 psi ¼ 6, Pa) for 15 s. A constant voltage of 25 kv and a detection wavelength of 200 nm were set for all experiments. Real sample preparation Landfill leachate (effluent of the landfill flushed by rain in the open air; Daye Landfill, Huangshi, China) and lake water samples (Sanjiao Lake and Qingshan Lake, Huangshi, China) were collected. Immediately after sampling, the samples were filtered through a 0.45 mm membrane (Tianjin Jinteng Instrument Factory, Tianjin, China), and stored at 48C in a refrigerator for subsequent use. Methods A solution containing the analytes was passed through the coal cinder microcolumn at a flow rate of 0.45 ml/min. The analytes trapped in the column were subsequently stripped by 0.20 ml of 10% (v/v) methanol 10 mmol/l disodium phosphate (Na 2 HPO 4 ) at a flow rate of 0.55 ml/min, and determined by MEKC UV. Results and Discussion Morphology of coal cinders The adsorption characteristic of a material is related to its physical morphology. Thus, the surface morphology of coal cinders is an important factor affecting its performance. Figure 1 shows the morphology of the coal cinders, characterized by SEM at different magnifications. The micrograph of coal cinders displays a roughened, porous structure, which can significantly improve the surface of the material and may be helpful for improving the extraction efficiency. CD-MEKC conditions To explore the possibility of improving the separation efficiency, ß-CD was added to the running electrolyte, which is composed of 5 mmol/l of borax containing 5% (v/v) methanol and 25 mmol/l of SDS at ph 9.5 (33). The results in Table I show that the numbers of theoretical plates for the analytes are all higher with the addition of ß-CD. The structure of b-cd was shown in the study by Martin Del Valle (34). It is a molecule with a hydrophilic exterior, which can dissolve in water, and an apolar cavity, which provides a hydrophobic matrix. As a result of this cavity, cyclodextrins are able to form inclusion complexes with a wide variety of hydrophobic guest molecules. One or two guest molecules can be entrapped by one, two or three cyclodextrins (34). Thus, the mechanism of retention for PE may be the hydrophobic interaction between the PE, which was 548 Sun et al.

3 Figure 1. SEM of coal cinders: magnified 200 times (A); magnified 1,000 times (B). Table I Effects of Additives on Number of Theoretical Plates and Peak Areas Running buffer Number of theoretical plates Peak areas DMP DEP DEHP DMP DEP DEHP 5 mmol/l borax containing 5% 1,675 2,120 7,149 20,547 30,302 12,507 (v/v) methanol, 25 mmol/l SDS at ph 9.5 (Buffer A) Buffer A þ 14 mmol/l ß-CD 24,719 22,168 36,428 24,254 34,960 14,736 entrapped by b-cd, and the inside surfaces of the cavity of ß-CD, leading to formation of the PE-ß-CD inclusion complex (35 36). Effect of b-cd on separation The effect of ß-CD concentration on separation efficiency was further investigated in the range of 0 18 mmol/l. The results showed that the electroosomotic flow decreased and the run times increased a little with an increase in the concentration of b-cd. With an increase in ß-CD concentration from 0 to 14 mmol/l, the peak areas and plate numbers for DMP, DEP and DEHP gradually increased, demonstrating that the resolution and selectivity were improved. However, the peak shapes broadened and tailed when ß-CD was over 16 mmol/l, which may be attributed to an overload of b-cd. Therefore, 14 mmol/l of ß-CD was selected as the optimal concentration. Development of coal cinder microcolumn extraction Because phthalates are neutral compounds, the ph of the medium does not affect their adsorption. The effects of several other experimental parameters upon the coal cinder microcolumn extraction of DMP, DEP and DEHP were thoroughly evaluated and optimized. Effect of adsorption flow rate of sample solution Analyte retention on the adsorbent depends upon the flow rate of the sample solution. The effect of sample flow rate on coal cinder adsorption was examined at a range of ml/min. The results showed that quantitative adsorption (over 90%) of DMP, DEP and DEHP was obtained at flow rate of less than 0.55 ml/min and decreased rapidly, owing to a decrease in the adsorption kinetics at a higher flow rate. Thus, a flow rate of 0.45 ml/min was employed in this work. Effect of desorption conditions To elute the analytes from the coal cinder, 10 mmol/l of Na 2 HPO 4 with different volume ratios of methanol was employed as the eluent in the study. The results showed that quantitative recovery for DMP, DEP and DEHP was obtained with 10% (v/v) methanol. Furthermore, the effect of a volume of 10 mmol/l Na 2 HPO 4 10% (v/v) methanol on quantitative recovery of the analytes was investigated, and the optimum volume was found to be 0.2 ml. The effect of desorption flow rate was investigated at the range of ml/min. The results showed that the quantitative recovery was obtained at the flow rates of ml/min. Thus, 0.55 ml/min was selected as the desorption flow rate. Effect of sample volume To assess the possibility of enriching low concentrations of analytes from large volumes, the maximum applicable sample volume was studied. Sample solutions of 5.0, 7.0, and 14.0 ml were examined, containing 0.05 mg each of DMP, DEP and DEHP, respectively, under the optimum conditions. The results showed that, within ml, recovery of the analytes was % and decreased rapidly to 64.3% with larger volumes. As mentioned previously, 0.2 ml of 10 mmol/l Na 2 HPO 4 10% (v/v) methanol was enough to elute the analytes, and the enrichment factor (EF) was 60 with 12.0 ml of sample. Reuse of the coal cinder microcolumn The coal cinder microcolumn could be used repeatedly after regeneration with distilled water. The stability and potential reuse of the adsorbent were assessed by monitoring the change in the recovery of the three analytes at each end of the adsorption elution cycle. After six adsorption elution cycles, the recovery of the analytes was almost constant within certain limits. Adsorption capacity Adsorption capacity determines how much the coal cinders were required to quantitatively concentrate the analytes from a given sample solution. Under the optimal conditions, the determination of dynamic adsorption capacity was performed based on the procedure recommended by Maquieira et al. (37). Determination of Three Phthalate Esters in Environmental Samples by Coal Cinder Extraction and Cyclodextrin Modified Micellar Electrokinetic Chromatography 549

4 Twelve milliliters of a series of DMP, DEP and DEHP concentrations (0.14, 0.16, 0.18, 0.20 and 0.22 mg/ml) were operated according to the general procedure. A breakthrough curve was obtained by plotting the DMP, DEP and DEHP concentrations (mg/ml) versus the micrograms of DMP, DEP and DEHP adsorbed per gram. The adsorption capacity values evaluated from the breakthrough curve were 17.1 mg/g for DMP, 17.0 mg/ g for DEP and 17.3 mg/g for DEHP. Separation performance: Evaluation of the combined methodology Figure 2 shows the electropherograms of 1.0 mg/l of analytes obtained by direct CD-MEKC and SPE-CD-MEKC under the optimum conditions. An obvious enhancement of sensitivity was observed, indicating the remarkable preconcentration abilities of coal cinders. The analytical characteristic data of SPE-CD-MEKC for the analytes are summarized in Table II. The calibration curves were established by using peak area versus concentration levels. The limits of detection (LODs), calculated as the analyte concentrations that produced peak areas with three times of signal-to-noise ratios (S/Ns), were 3.07 ng/ml for DMP, 2.07 ng/ml for DEP and 4.06 ng/ml for DEHP. The relative standard deviations (RSDs) of peak areas of DMP, DEP and DEHP were 5.27, 4.34, and7.32%, respectively (concentration ¼ 20 ng/ml, n ¼ 9). For a comparison of the analytical characteristics of the SPE-CD-MEKC, the merits of various methods for the separation and determination of PEs are listed in Table III. As shown in this Figure 2. Electropherograms of 1.0 mg/l of DMP, DEP and DEHP obtained by using: direct CD-MEKC (A); SPE-CD-MEKC (B). Running buffer: 5 mmol/l of borax, 5% (v/v) methanol, 25 mmol/l SDS at ph 9.5 with 14 mmol/l ß-CD. SPE conditions: sample solution flow rate of 0.45 ml/min, eluent flow rate of 0.55 ml/min, desorpted by 0.2 ml of 10 mmol/lna 2 HPO 4 with 10% methanol and injection time of 15 s. Table II Analytical Characteristics of the SPE-CD-MEKC Method for the Determination of PEs Analyte Concentration range (ng/ml) Regression equation Correlation coefficient RSD* (%) LOD (ng/ml) DMP 20 2,000 A ¼ þ C DEP 20 2,000 A ¼ 93.2 þ C DEHP 20 2,000 A ¼ þ C *Concentration ¼ 20 ng/ml; n ¼ 9. EF of 60. Figure 3. Electropherograms of landfill leachate obtained by using: direct MEKC (A); unspiked SPE-CD-MEKC (B); spiked SPE-CD-MEKC (C). Running buffer was the same as in Figure 1; SPE conditions were the same as in Figure 1B; injection time was 15 s; injection pressure was 0.5 psi (1 psi ¼ 6, Pa). Table III Figures of Merit of Other Methods for the Analysis of PEs Comparison of proposed method with other methods Sample Analyte* Methods Pretreatment method LOD (ng/ml) Reference Soil DMP, DEP, BBP, DnBP, DnOP and DEHP HPLC Microwave assisted extraction Cosmetics DMP, DnBP, DCHP and DnOP HPLC Polymer monolith microextraction Standard solutions DMP, DEP and DBP MEKC 400 1, Soil leachate DMP, DEP, DBP, DEHP and DnOP MEKC Liquid-phase extraction Water samples DMP, DEP, DnBP, DEHP and DOP SPE-LC Nylon6 nanofibers, mat-based Aqueous sample DBP SPE-GC MS Molecularly imprinted polymer Food packaging bags DMP, DEP, DBP, DEHP and DOP MEKC Fruit jellies DMP, DEP, DPP, BBP and DCHP SPE-HPLC MS Dispersive Environmental samples DMP, DEP and DEHP SPE-CD-MEKC Coal cinder microcolumn This work Comparison of coal cinders with commercially available SPE cartridges Sample Analyte Methods Cartridge LOD (ng/ml) Reference Human serum DMP, DEP, DBP, BBP, DEHP and DNOP SPE-GC MS Waters Oasis MAX SPE cartridges Sludge and vegetables DMP, DEP, DBP, BBP, DEHP and DOP SPE-GC MS Florisil SPE cartridge Water BBP and DEHP SPE-LC Polystyrene column Wine DMP, DEP, DBP, BBP, DEHP and ibp SPE-GC MS C18 column Packaging film DMP, DEP, DBP, DEHP, BBP and DOP SPE-GC MS Waters Oasis MAX SPE cartridges Environmental samples DMP, DEP and DEHP SPE-CD-MEKC Coal cinder microcolumn This work *Benzylbutyl phthalate (BBP), dibutyl phthalate (DBP), dicyclohexyl phthalate (DCHP), dioctyl phthalate (DOP), di-n-butyl phthalate (DnBP), di-n-octyl phthalate (DnOP), dipentyl phthalate (DPP), isobutyl phthalate (ibp). 550 Sun et al.

5 Table IV Analytical Results of PEs in Landfill Leachate and Water Samples by SPE-CD-MEKC* Sample Added (mg/l) DMP DEP DEHP Found (mg/l) Recovery (%) Found (mg/l) Recovery (%) Found (mg/l) Recovery (%) Landfill leachate Qingshan Lake 0 ND ND ND Sanjiao Lake 0 ND ND ND *ND: Not detected. For three determinations. table, LODs of this method are more than an order of magnitude lower than those of methods described in studies by Guo et al. (18), Morales-Cid et al. (19) and Chen et al. (33), although they are much higher than those reported by Yao et al. (11), Su et al. (12), Takeda et al. (20), He et al. (28) and Ma et al. (36). Compared with methods of commercial cartridge SPE-GC MS (4, 38, 40, 41), polymer monolith microextraction HPLC (12) and dispersive SPE-HPLC MS (36) for the detection of PEs, the coal cinder SPE-CD-MEKC technique is simpler and cheaper. Real sample analysis The developed SPE-CD-MEKC method was applied to determine DMP, DEP and DEHP in landfill leachate and water samples under the optimum conditions. Figure 3 shows the electropherograms of DMP, DEP and DEHP in a landfill leachate sample. Figure 3A shows an unspiked landfill leachate sample by direct CD-MEKC; Figure 3B shows an unspiked landfill leachate sample by SPE-CD-MEKC; and Figure 3C shows a spiked landfill leachate sample by SPE-CD-MEKC. After the coal cinder SPE, a very sensitive, clean and obvious electropherogram containing only DMP, DEP and DEHP peaks is shown in Figure 3B. The results (summarized in Table IV) show that the recovery values of DMP, DEP and DEHP are acceptable: between 90.0 and 110.0%. Concluding Remarks Coal cinder has been used to separate and preconcentrate DMP, DEP and DEHP in environmental samples, resulting in a 60-fold enhancement in the sensitivity of CD-MEKC UV for the determination of DMP, DEP and DEHP. The separation efficiency and sensitivity of MEKC have been also improved by using ß-CD as the electrophoresis additive. A cheap, simple and sensitive SPE-CD-MEKC method has been established for the separation and determination of DMP, DEP and DEHP in landfill leachate and water samples, with satisfactory results. Acknowledgments This project was financially supported by National Nature Science Foundation of China (No , ), Education Committee of Hubei Province (D ), Young and Middle-Aged Elitists Scientific and Technological Innovation Team Project of Hubei Education Department of China under Grant (T201007). References 1. Singh, S., Li, S.S.; Phthalates: Toxicogenomics and inferred human diseases; Genomics, (2011); 97: Mackintosh, C.E., Maldonado, J., Hong, J., Hoover, N., Chong, A., Ikonomou, M.G., et al.; Distribution of phthalate esters in a marine aquatic food web: Comparison to polychlorinated biphenyls; Environmental Science & Technology, (2004); 38: Bradley, O.C., Stephen, R.S.; Review of emerging organic contaminants in biosolids and assessment of international research priorities for the agricultural use of biosolids; Environment International, (2011); 37: Guo, Z.Y., Gai, P.P., Duan, J., Zhai, J.X., Zhao, S.S., Wang, S., et al.; Simultaneous determination of phthalates and adipates in human serum using gas chromatography mass spectrometry with solidphase extraction; Biomedical Chromatography, (2010); 24: Ferguson, K.K., Loch-Caruso, R., Meeker, J.D.; Urinary phthalate metabolites in relation to biomarkers of inflammation and oxidative stress: NHANES ; Environmental Research, (2011); 111: Lin, S., Ku, H.Y., Su, P.H., Chen, J.W., Huang, P.C., Angerer, J., et al.; Phthalate exposure in pregnant women and their children in central Taiwan; Chemosphere, (2011); 82: Marke ta, J., Roman, S.; Removal of phthalates from aqueous solution by different adsorbents: A short review; Journal of Environmental Management, (2012); 94: Vicent, Y.S., Ye, X.Y., Antonia, M.C.; Methods for the determination of biomarkers of exposure to emerging pollutants in human specimens; Trends in Analytical Chemistry, (2012); 38: Huang, L.P., Lee, C.C., Hsu, P.C., Shih, T.S.; The association between semen quality in workers and the concentration of di(2-ethylhexyl) phthalate in polyvinyl chloride pellet plant air; Journal of Exposure Analysis and Environmental Epidemiology, (2011); 96: Guo, Y., Alomirah, H., Cho, H.S., Minh, T.B., Mohd, M.A., Nakata, H., et al.; Occurrence of phthalate metabolites in human urine from several Asian countries; Environmental Science & Technology, (2011); 45: Yao, H.B., Han, G.J., Liu, G.X.; Determination of phthalate esters in soil samples by microwave assisted extraction and high performance liquid chromatography; Bulletin of Environmental Contamination and Toxicology, (2010); 85: Su, R.Y., Zhao, X.W., Li, Z.Y.; Poly(methacrylic acid-co-ethylene glycol dimethacrylate) monolith microextraction coupled with high performance liquid chromatography for the determination of phthalate esters in cosmetics; Analytica Chimica Acta, (2010); 676: Determination of Three Phthalate Esters in Environmental Samples by Coal Cinder Extraction and Cyclodextrin Modified Micellar Electrokinetic Chromatography 551

6 13. Yan, Y., Du, J.J., Zhang, X.G.; Ultrasound-assisted dispersive liquidliquid microextraction coupled with capillary gas chromatography for simultaneous analysis of nine pyrethroids in domestic wastewaters; Journal of Separation Science, (2010); 33: Bergh, C., Torgrip, R., Ostman, C.; Simultaneous selective detection of organophosphate and phthalate esters using gas chromatography with positive ion chemical ionization tandem mass spectrometry and its application to indoor air and dust; Rapid Communications in Mass Spectrometry, (2010); 24: Ostrovsky, I., Cabala, R., Kubinec, R.; Determination of phthalate sum in fatty food by gas chromatography; Food Chemistry, (2010); 124: Kondo, F., Ikai, Y., Hayashi, R.; Determination of five phthalate monoesters in human urine using gas chromatography-mass spectrometry; Bulletin of Environmental Contamination and Toxicology, (2010); 85: Rios, J.J., Morales, A., Marquez-Ruiz, G.; Headspace solid-phase microextraction of oil matrices heated at high temperature and phthalate esters determination by gas chromatography multistage mass spectrometry; Talanta, (2010); 80: Guo, B.Y., Wen, B., Shan, X.Q., Zhang, S.Z., Lin, J. M.; Separation and determination of phthalates by micellar electrokinetic chromatography; Journal of Chromatography A, (2005); 1095: Morales-Cid, G., Cardenas, S., Simanet, B.M., Valcárcel, M.; Comparison of aromatic and alkyl micelles for the electrokinetic determination of phthalates in virgin olive oil; Electrophoresis, (2009); 30: Takeda, S., Wakida, S., Yamane, M., Kawahara, A., Higashi, K.; Migration behavior of phthalate esters in micellar electrokinetic chromatography with or without added methanol; Analytical Chemistry, (1993), 65(18): Thormann, W., Aebi, Y., Lanz, M., Caslavska, J.; Capillary electrophoresis in clinical toxicology; Forensic Science International, (1998); 92: Wu, Y.W., Jiang, Y.Y., Liu, J. F., Xiong, K.; Cloud point extraction combined with micellar electrokinetic capillary chromatography determination of benzophenones in cosmetic matrix; Electrophoresis, (2008); 29: Yan, H., Liu, B., Du, J., Row, K.H.; Simultaneous determination of four phthalate esters in bottled water using ultrasound-assisted dispersive liquid-liquid microextraction followed by GC-FID detection; Analyst, (2010); 135: Zhou, Q.X., Mao, J.L., Xiao, J.P.; Determination of paraquat and diquat preconcentrated with N doped TiO2 nanotubes solid phase extraction cartridge prior to capillary electrophoresis; Analytical Methods, (2010); 2: Ding, Y.S., Rogers, K.; Determination of haloacetic acids in water using solid-phase extraction/microchip capillary electrophoresis with capacitively coupled contactless conductivity detection; Electrophoresis, (2010); 31: Zhang, S.W., Zou, C.J., Luo, N.; Determination of urinary 8-hydroxy-2 -deoxyguanosine by capillary electrophoresis with molecularly imprinted monolith in-tube solid phase microextraction; Chinese Chemical Letters, (2010); 21: Allan, S.H.; The SPE international award address 1975 polymerization by oxidative coupling An historical review; Polymer Engineering & Science, (1976); 16: He, J.A., Lv, R.H., Zhan, H.J.; Preparation and evaluation of molecularly imprinted solid-phase micro-extraction fibers for selective extraction of phthalates in an aqueous sample; Analytica Chimica Acta, (2010); 674: Asadollahzadeh, H., Noroozian, E., Maghsoudi, S.; Solid-phase microextraction of phthalate esters from aqueous media by electrochemically deposited carbon nanotube/polypyrrole composite on a stainless steel fiber; Analytica Chimica Acta, (2010); 669: Zhang, S.X., Niu, H.Y., Cai, Y.Q.; Barium alginate caged Fe3O4@C18 magnetic nanoparticles for the pre-concentration of polycyclic aromatic hydrocarbons and phthalate esters from environmental water samples; Analytica Chimica Acta, (2010); 665: Yang, J., Wang, S., Lu, Z., Yang, J., Lou, S.; Converter slag-coal cinder columns for the removal of phosphorous and other pollutants; Journal of Hazardous Materials, (2009); 168: Wu, Y.W., Jiang, F., Chen, L., Zheng, J., Deng, Z., Tao, Q., et al.; Determination of phenylenediamine isomers in hair dyes by coal cinders micro-column extraction and MEKC; Analytical and Bioanalytical Chemistry, (2011); 400: Chen, H., Jia, R., Jia, L.; Analysis of phthalates in food-packaging bags by micellar electrokinetic capillary chromatography; Chinese Journal of Analytical Chemistry, (2007); 23: Martin Del Valle, E.M.; Cyclodextrins and their uses: A review; Process Biochemistry, (2004); 39: Wang, P., Ren, J.; Separation of purine and pyrimidine bases by capillary electrophoresis using beta-cyclodextrin as an additive; Journal of Pharmaceutical and Biomedical Analysis, (2004); 34: Ma, Y., Hashi, Y., Ji, F., Lin, J. M.; Determination of phthalates in fruit jellies by dispersive SPE coupled with HPLC-MS; Journal of Separation Science, (2010); 33: Maquieira, A., Elmahadi, H.A.M., Puchades, R.; Immobilized cyanobacteria for on-line trace metal enrichment by flow injection atomic absorption; Analytical Chemistry, (1994); 66: Sablayrolles, C., Vignoles, M.M., Benanou, D., Patria, P., Treilhou, M.; Development and validation of methods for the trace determination of phthalates in sludge and vegetables; Journal of Chromatography A, (2005); 1072: Jara, S., Lysebo, C., Greibrokk, T., Lundanes, E.; Determination of phthalates in water samples using polystyrene solid-phase extraction and liquid chromatography quantification; Analytica Chimica Acta, (2000); 407: Carlo, M.D., Pepe, A., Sacchetti, G., Compagnone, D., Mastrocola, D., Cichelli, A.; Determination of phthalate esters in wine using solidphase extraction and gas chromatography mass spectrometry; Food Chemistry, (2008); 111: Guo, Z.Y., Sui, W., Wei, D.Y., Wang, M.L., Zhang, H.N., Gai, P.P., et al.; Development and application of a method for analysis of phthalates in ham sausages by solid-phase extraction and gas chromatography-mass spectrometry; Meat Science, (2010) 84: Sun et al.