Meng Mei

Monitoring of selected estrogen mimics in complicated samples using polymeric ionic liquid-based multiple monolithic fiber solid-phase microextraction combined with high-performance liquid chromatography

A convenient, rapid, sensitive and environmentally friendly method for simultaneous monitoring of six estrogen mimics (bisphenol A, diethylstilbestrol, dienestrol, hexestrol, octylphenol and nonylphenol) in water and milk samples was developed by coupling multiple monolithic fiber solid-phase microextraction (MMF-SPME) to high performance liquid chromatography with diode array detection. The MMF-SPME based on polymeric ionic liquid-based monolith as extractive medium was used to concentrate target analytes. Because there were multiple interactions between adsorbent and analytes, the MMF-SPME exhibited a high extractive capability toward analytes. To obtain optimum extraction performance, several extraction parameters including desorption solvent, pH value and ionic strength in sample matrix, extraction and desorption time were investigated and discussed. Under the optimized extraction conditions, the limits of detection (S/N=3) of the proposed method were 0.040-0.11 μg/L in water and in milk samples. Satisfactory linearity was achieved for analytes with the correlation coefficients (r) above 0.99. Excellent method reproducibility was achieved by evaluating the repeatability, intermediate precision and MMF-to-MMF reproducibility with relative standard deviations (RSDs) of both less than 10%. Finally, the proposed method was successfully applied to the determination of estrogen mimics in several milk and environmental water samples. Recoveries obtained for the determination of six target analytes in spiking samples ranged from 75.6% to 118%, with RSD below 10% in all cases.

Multiple monolithic fiber solid-phase microextraction: A new extraction approach for aqueous samples

A novel multiple monolithic fiber solid-phase microextraction (MMF-SPME) was designed and prepared. Two steps were involved in the preparation of MMF-SPME. Firstly, single thin fiber (0.5mm in diameter) was prepared by co-polymerization of vinylimidazole and ethylene dimethacrylate. Secondly, several thin fibers were bound together to obtain the MMF assembly. The extraction and desorption dynamics of MMF-SPME with different numbers of fibers were studied in detail. In order to demonstrate the usability of the new MMF-SPME, the extraction performance of MMF-SPME for 2-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol was investigated in direct SPME mode. Results indicated that aqueous samples could form convection effectively within MMF-SPME because there were gaps between fibers. The extraction procedure was accelerated by the convection. At the same time, the MMF-SPME possessed high extraction capacity because more sorbent was employed. Under the optimized extraction conditions, low detection limits (S/N=3) and quantification limits (S/N=10) for the target analytes were achieved within the range of 0.13-0.29 μg/L and 0.44-0.98 μg/L, respectively. The MMF-SPME also showed a very long lifespan and good repeatability. Finally, the MMF-SPME was successfully applied to the analysis of tap, lake and ground water samples with spiked recoveries in the range of 73.8-101%.

Sensitive monitoring of benzoylurea insecticides in water and juice samples treated with multiple monolithic fiber solid-phase microextraction and liquid chromatographic analysis.

In present study, a convenient, sensitive and environmentally friendly method for the determination of five benzoylurea insecticides (BUs) in water and juice samples was developed. To extract trace benzoylurea insecticides effectively, poly(methacrylic acid-co-ethylene dimethacrylate) monolith was prepared and used as the sorbent of multiple monolithic fiber solid-phase microextraction (MMF-SPME). The influences of preparation conditions of monolith and extraction parameters of MMF-SPME on BUs were studied thoroughly. Under the optimized conditions, the combination of MMF-SPME with high performance liquid chromatography-diode array detection (MMF-SPME-HPLC-DAD) showed expected analytical performance for target analytes. The limits of detection (S/N=3) of the developed method were 0.026-0.075 μg L(-1) in water and 0.053-0.29 μg L(-1) in juice samples. Good linearity was obtained for analytes with the correlation coefficients (R(2)) above 0.99. Satisfactory repeatability and reproducibility was achieved, with relative standard deviations (RSD) of both less than 10%. Finally, the established MMF-SPME-HPLC-DAD method was successfully applied for the determination of BUs residues in juice and environmental water samples. Recoveries obtained for the determination of BUs in spiking samples ranged from 65.1% to 118%, with RSD below 10% in all cases.

Sensitive monitoring of trace nitrophenols in water samples using multiple monolithic fiber solid phase microextraction and liquid chromatographic analysis

In this work, a simple, efficient and environmentally friendly method-multiple monolithic fiber solid-phase microextraction (MMF-SPME) combining with high-performance liquid chromatography (HPLC) was first established for the determination of six trace nitrophenols in water samples. In order to prepare MMF-SPME, 1-allyl-3-methylimidazolium bis [(trifluoro methyl) sulfonyl] imide was co-polymerized with ethylene dimethacrylate to get single thin fiber (0.5 mm in diameter). Subsequently, four thin fibers were bound together to obtain the MMF-SPME. The effect of preparation conditions of MMF-SPME on the extraction performance was investigated in detail. In order to obtain the optimal extraction conditions of MMF-SPME for nitrophenols, several extractive parameters, including desorption solvent, extraction and desorption time, pH values and ionic strength in sample matrix were optimized. Under the optimum conditions, the linear ranges of 4-nitrophenol, 2,4-dinitrophenol, 5-methyl-2-nitrophenol, 5-methoxyl-2-nitrophenol were 0.5-200 µg/L and 1.0-200 µg/L for 2-nitrophenol and 4-tertbutyl-2-nitrophenol. The limits of detection (S/N=3) for the target analytes were 0.075-0.27 µg/L. At the same time, excellent method reproducibility was achieved in terms of intra- and inter-day precisions, indicated by the RSDs of both <10.0%, respectively. Finally, the proposed method was successfully used to detect nitrophenols in different environmental water samples. Satisfactory recoveries ranged from 82.6% to 116% and the RSDs for reproducibility were less than 10% for target analytes in all real samples.

Multiple monolithic fiber solid‐phase microextraction based on a polymeric ionic liquid with high‐performance liquid chromatography for the determination of steroid sex hormones in water and urine

The development of a simple and sensitive analytical approach that combines multiple monolithic fiber solid-phase microextraction with liquid desorption followed by high-performance liquid chromatography with diode array detection is proposed for the determination of trace levels of seven steroid sex hormones (estriol, 17β-estradiol, testosterone, ethinylestradiol, estrone, progesterone and mestranol) in water and urine matrices. To extract the target analytes effectively, multiple monolithic fiber solid-phase microextraction based on a polymeric ionic liquid was used to concentrate hormones. Several key extraction parameters including desorption solvent, extraction and desorption time, pH value and ionic strength in sample matrix were investigated in detail. Under the optimal experimental conditions, the limits of detection were found to be in the range of 0.027-0.12 μg/L. The linear range was 0.10-200 μg/L for 17β-estradiol, 0.25-200 μg/L estriol, ethinylestradiol and estrone, and 0.50-200 μg/L for the other hormones. Satisfactory linearities were achieved for analytes with the correlation coefficients above 0.99. Acceptable method reproducibility was achieved by evaluating the repeatability and intermediate precision with relative standard deviations of both less than 8%. The enrichment factors ranged from 54- to 74-fold. Finally, the proposed method was successfully applied to the analysis of steroid sex hormones in environmental water samples and human urines with spiking recoveries ranged from 75.6 to 116%.

Preparation of monolithic fibers for the solid-phase microextraction of chlorophenols in water samples

Monolithic fibers were synthesized and applied for the solid-phase microextraction and determination of chlorophenols in environmental water samples by coupling with HPLC. The fibers were prepared by copolymerization of vinylimidazole and ethylene dimethacrylate as functional monomer and cross-linker, respectively. The effect of the preparation conditions of monolithic fibers on the extraction efficiencies was investigated in detail. Several characteristic techniques, such as elemental analysis, infrared spectroscopy, mercury-intrusion porosimetry, and SEM were used to characterize the monolithic material. The effect of the extraction parameters, including desorption solvent, extraction and desorption time, pH values, and ionic strength in sample matrix on the extraction performance was investigated thoroughly. Under the improved extraction conditions, the linear ranges of 2-chlorophenol, 2,4-dichlorophenol and pentachlorophenol were 1.0-200 μg/L and 2.0-200 μg/L for 2,4,6-trichlorophenol. The detection limits (S/N = 3) were in the range of 0.16-0.45 μg/L, the RSDs for intraday and interday precisions were <7.0%. Finally, the proposed method was successfully used to detect different environmental water samples. The recoveries of spiked water samples were ranged from 90.0 to 115%. At the same time, satisfactory repeatability was achieved with RSDs < 9.0%.

Determination of fluoroquinolones in environmental water and milk samples treated with stir cake sorptive extraction based on a boron-rich monolith.

In this study, a new stir cake sorptive extraction using a boron-rich monolith as the adsorbent was prepared by the in situ copolymerization of vinylboronic anhydride pyridine complex and divinylbenzene. The effect of preparation parameters, including the ratio of vinylboronic anhydride pyridine complex and divinylbenzene, monomer mixture, and porogen solvent, on extraction performance was investigated thoroughly. The physicochemical properties of the adsorbent were characterized by infrared spectroscopy, scanning electron microscopy, and mercury intrusion porosimetry. Several conditions affecting the extraction efficiency were investigated in detail. Under the optimized conditions, a convenient and sensitive method for the determination of trace fluoroquinolones residues in water and milk samples was established by coupling stir cake sorptive extraction with high-performance liquid chromatography and diode array detection. The limits of detection for the target compounds were 0.10-0.26 and 0.11-0.22 μg/L for water and milk samples, respectively. In addition, the developed method showed good linearity, repeatability, and precision. Finally, the proposed method was successfully applied for the detection of trace fluoroquinolones residues in environmental water and milk samples. Satisfactory recoveries were obtained for the determination of fluoroquinolones in spiking samples that ranged from 68.8 to 120%, with relative standard deviations below 10% in all cases.

Magnetism-Enhanced Monolith-Based In-Tube Solid Phase Microextraction

Monolith-based in-tube solid phase microextraction (MB/IT-SPME) has received wide attention because of miniaturization, automation, expected loading capacity, and environmental friendliness. However, the unsatisfactory extraction efficiency becomes the main disadvantage of MB/IT-SPME. To overcome this circumstance, magnetism-enhanced MB/IT-SPME (ME-MB/IT-SPME) was developed in the present work, taking advantage of magnetic microfluidic principles. First, modified Fe3O4 nanoparticles were mixed with polymerization solution and in situ polymerized in the capillary to obtain a magnetic monolith extraction phase. After that, the monolithic capillary column was placed inside a magnetic coil that allowed the exertion of a variable magnetic field. The effects of intensity of magnetic field, adsorption and desorption flow rate, volume of sample, and desorption solvent on the performance of ME-MB/IT-SPME were investigated in detail. The analysis of six steroid hormones in water samples by the combination of ME-MB/IT-SPME with high-performance liquid chromatography with diode array detection was selected as a paradigm for the practical evaluation of ME-MB/IT-SPME. The application of a controlled magnetic field resulted in an obvious increase of extraction efficiencies of the target analytes between 70% and 100%. The present work demonstrated that application of different magnetic forces in adsorption and desorption steps can effectively enhance extraction efficiency of MB/IT-SPME systems.

Preparation of a new polymeric ionic liquid-based sorbent for stir cake sorptive extraction of trace antimony in environmental water samples

In this work, a new polymeric ionic liquid (PIL)-based sorbent was prepared by in-situ polymerization of 3-(1-ethyl imidazolium-3-yl) propyl-methacrylamido bromide and ethylene dimethacrylate and was used as medium for stir cake sorptive extraction (SCSE) of trace antimony in environmental water samples. The sorbent EPBED was characterized with infrared spectroscopy, elemental analysis, scanning electron microscopy and mercury intrusion porosimetry. A method for determination of trace antimony in water samples was developed based on the combination of SCSE/EPBED and hydride generation atomic fluorescence spectrometry (HG-AFS). Under the optimal extraction conditions, the linear dynamic range of developed method was found to be 0.20-100.0μg/L with good coefficients of correlation (R2=0.9904) and LOD value as low as 0.084μg/L. The method showed good reproducibility of results in terms of intra- and inter-day precisions with corresponding relative standard deviations (RSDs) of less than 9%. Recoveries obtained for the determination of antimony in spiked samples ranged from 80.4% to 107% with RSDs below 10% in all cases.

Sensitive determination of estrogens in environmental waters treated with polymeric ionic liquid-based stir cake sorptive extraction and liquid chromatographic analysis

A simple, sensitive and environmentally friendly method using polymeric ionic liquid-based stir cake sorptive extraction followed by high performance liquid chromatography with diode array detection (HPLC/DAD) has been developed for efficient quantification of six selected estrogens in environmental waters. To extract trace estrogens effectively, a poly (1-ally-3-vinylimidazolium chloride-co-ethylene dimethacrylate) monolithic cake was prepared and used as the sorbent of stir cake sorptive extraction (SCSE). The effects of preparation conditions of sorbent and extraction parameters of SCSE for estrogens were investigated and optimized. Under optimal conditions, the developed method showed satisfactory analytical performance for targeted analytes. Low limits of detection (S/N=3) and quantification limits (S/N=10) were achieved within the range of 0.024-0.057 µg/L and 0.08-0.19 µg/L, respectively. Good linearity of method was obtained for analytes with the correlation coefficients (R(2)) above 0.99. At the same time, satisfactory method repeatability and reproducibility was achieved in terms of intra- and inter-day precisions, respectively. Finally, the established SCSE-HPLC/DAD method was successfully applied for the determination of estrogens in different environmental water samples. Recoveries obtained for the determination of estrogens in spiked samples ranged from 71.2% to 108%, with RSDs below 10% in all cases.