Liquid-liquid-liquid microextraction with automated movement of the acceptor and the donor phase for the extraction of phenoxyacetic acids prior to liquid chromatography detection

A simple liquid-liquid-liquid microextraction with automated movement of the acceptor and the donor phase (LLLME/AMADP) technique is described for the quantitative determination of five phenoxyacetic acids in water using a disposable and ready to use hollow fiber. The target compounds were extracted from the acidified sample solution (donor phase) into the organic solvent residing in the pores of the hollow fiber and then back extracted into the alkaline solution (acceptor phase) inside the lumen of the hollow fiber. The fiber was held by a conventional 10-microl syringe. The acceptor phase was sandwiched between the plunger and a small volume of the organic solvent (microcap). The acceptor solution was repeatedly moved in and out of the hollow fiber assisted by a programmable syringe pump. This repeated movement provides a fresh acceptor phase to come in-contact with the organic phase and thus enhancing extraction kinetics leading to high enrichment of the analytes. The microcap separates the aqueous acceptor phase and the donor phase in addition of being partially responsible for mass transfer of the analytes from donor solution (moving in and out of the hollow fiber from the open end of the fiber) to the acceptor solution. Separation and quantitative analyses were then performed using liquid chromatography (LC) with ultraviolet (UV) detection at 280 nm. Various parameters affecting the extraction efficiency viz. type of organic solvent used for immobilization in the pores of the hollow fiber, extraction time, stirring speed, effect of sodium chloride, and concentration of donor and acceptor phases were studied. Repeatability (RSD, 3.2-7.4%), correlation coefficient (0.996-0.999), detection limit (0.2-2.8 ng ml(-1)) and enrichment factors (129-240) were also investigated. Relative recovery (87-101%) and absolute recoveries (4.6-13%) have also been calculated. The developed method was applied for the analysis of river water.     

Dynamic three-phase hollow fiber microextraction based on two immiscible organic solvents with automated movement of the acceptor phase

Dynamic three-phase hollow fiber liquid-liquid-liquid microextraction (HF-LLLME) based on two immiscible organic solvents, with automated movement of organic acceptor phase to facilitate mass transfer was introduced for the first time. Polycyclic aromatic hydrocarbons were used as model compounds and extracted from water and soil samples. The extraction involved filling an 8 cm length of hollow fiber with 25 μL of organic acceptor solvent using a microsyringe, followed by impregnation of the pores in the fiber wall with n-dodecane. The fiber was then immersed in 20 mL of aqueous sample solution. During extraction, the organic acceptor phase was repeatedly moved in the lumen of the hollow fiber by movement of the syringe plunger controlled by programmable syringe pump. Following this microextraction, 2 μL of organic acceptor phase was injected into gas chromatography-flame ionization detector. This new technique provided up to 554-fold preconcentration of the analytes under the optimized conditions. Good repeatabilities (with RSDs ≤8.4%) were obtained. Detection limits were in the range of 0.2-0.5 μg/L. The utilization of the proposed method for extraction of the polycyclic aromatic hydrocarbons from different real samples (such as water and soil samples) also gave good precision and recovery.     

Extraction of hydroxyaromatic compounds in river water by liquid-liquid-liquid microextraction with automated movement of the acceptor and the donor phase

Liquid-liquid-liquid microextraction with automated movement of the acceptor and the donor phase technique is described for the extraction of six hydroxyaromatic compounds in river water using a disposable and ready to use hollow fiber. Separation and quantitative analyses were performed using LC with UV detection at 254 nm. Analytes were extracted from the acidified sample solution (donor phase) into the organic solvent impregnated in the pores of the hollow fiber and then back extracted into the alkaline solution (acceptor phase) inside the lumen of the hollow fiber. The fiber was held by a conventional 10 microL LC syringe. The acceptor phase was sandwitched between the plunger and a small volume of the organic solvent (microcap). The acceptor solution was repeatedly moved in and out of the hollow fiber using a syringe pump. This movement provides a fresh acceptor phase to come in contact with the organic phase and thus enhancing extraction kinetics thereby leading to the improvement in enrichment of the analytes. The microcap separates the acceptor phase and the donor phase in addition to being partially responsible for mass transfer of the analytes from the donor solution to the acceptor solution. Under stirring, a fresh donor phase will enter through the open end of the fiber that will also contribute to the mass transfer. Various parameters affecting the extraction efficiency viz type of organic solvent, extraction time, stirring speed, effect of sodium chloride, and concentration of donor and acceptor phases were studied. RSD (3.9-5.6%), correlation coefficient (0.995-0.997), detection limit (2.0-51.2 ng/mL), enrichment factor (339-630), relative recovery (93.2-97.9%), and absolute recovery (33.9-63.0%) have also been investigated. The developed method was applied for the analysis of river water.     

Electrokinetic migration of acidic drugs across a supported liquid membrane

Electrokinetic cross membrane extraction of acidic drugs was demonstrated for the first time. The acidic drugs were extracted from an alkaline aqueous donor solution (300 microl), through a thin supported liquid membrane of 1-heptanol sustained in the pores of the wall of a porous hollow fiber, and into an aqueous alkaline acceptor solution (30 microl) present inside the lumen of the hollow fiber by the application of a d.c. electrical potential. The negative electrode was placed in the donor solution, and the positive electrode was placed in the acceptor solution. Optimal extractions were accomplished with 1-heptanol as the supported liquid membrane, with 50 V as the driving force, and with pH 12.0 in both the donor and acceptor solutions, respectively (NaOH). Equilibrium extraction conditions were obtained after 5 min of operation with the whole assembly agitated at 1200 rpm. Eleven different acidic drugs were extracted with recovery values between 8 and 100%, and initial data supported that electrokinetic cross membrane extraction provided repeatable data and linear response between original donor concentration and final acceptor concentration of the acidic model compounds.     

Liquid-liquid-liquid microextraction of nitrophenols with a hollow fiber membrane prior to capillary liquid chromatography

A simple liquid-liquid-liquid microextraction device utilizing a 2 cm x 0.6 mm I.D. hollow fiber membrane was used to preconcentrate nitrophenols from water sample prior to capillary liquid chromatography (cLC) analysis. The extraction procedure was induced by the pH difference inside and outside the hollow fiber. The donor phase outside the hollow fiber was adjusted to pH approximately 1 with HCl; the acceptor phase was NaOH solution used at various concentrations. Organic solvent was immobilized into the pores of the hollow fiber. With stirring, the neutral nitrophenols outside the fiber were extracted into the organic solvent, then back extracted into 2 microl of basic acceptor solution inside the fiber. The acceptor phase was then withdrawn into a microsyringe and injected into the cLC system directly. This technique used a low-cost disposable extraction "device" and is very convenient to operate. Up to 380-fold enrichment of analytes could be achieved. This procedure could also serve as a sample clean-up step because large molecules and basic compounds were not extracted into the acceptor phase. The RSD (n=6) was less than 6.2%, while the linear calibration range was from 1 to 200 microg/ml with r>0.998. The procedure was applied to the analysis of seawater.     

Development and application of microporous hollow fiber protected liquid-phase microextraction via gaseous diffusion to the determination of phenols in water

A new organic solvent-free microextraction technique termed liquid-gas-liquid microextraction (LGLME) was developed. In this technique, a small amount (6 microl) of aqueous acceptor solution (0.5M NaOH) is introduced into the channel of a 2.65 cm polypropylene hollow fiber. The hollow fiber is then immersed in an aqueous sample donor solution. The aqueous acceptor phase in the channel of the hollow fiber is separated from the sample solution by the hydrophobic microporous hollow fiber wall with air inside its pores. The analytes (phenols) passed through the microporous hollow fiber membrane by gas diffusion and were then trapped by the basic acceptor solution. After extraction, the acceptor solution was withdrawn into a microsyringe and injected into a capillary electrophoresis sample vial for subsequent analysis. Limits of detection of between 0.5 and 10 microg/l for eight phenols could be achieved. The relative standard deviations (n=6) of this technique between 2.7 and 7.6%. The technique also provides good enrichment factors for all the eight analytes.     

ADSORPTION OF UO2 2+ BY POLYETHYLENE HOLLOW FIBER MEMBRANE WITH AMIDOXIME GROUP

The polyethylene (PE) membrane was prepared by the radiation-induced grafting of acrylonitrile (AN) onto PE hollow fiber and by the subsequent amidoximation of cyano groups in poly-AN graft chains. The adsorption characteristics of the chelating hollow fiber membrane was examined as the solution of UO₂ ²⁺ permeated across the chelating hollow fiber membrane. The inner and outer diameter increased with an increasing grafting yield, whereas, the pure water flux and pore diameter decreased with an increasing grafting yield. The adsorption of UO₂ ²⁺ by the chelating hollow fiber membranes increased with an increasing amidoxime group. The adsorbed amount of UO₂ ²⁺ in the uranyl acetate solution was higher than that in the uranyl nitrate solution. The adsorbed amount of UO₂ ²⁺ is higher than that of Cu²⁺ when the solution of UO₂ ²⁺ and Cu²⁺ permeated across the chelating membrane, respectively. The adsorption characteristics of UO₂ ²⁺ by the amidoxime group-chelating fiber membrane in the presence of Na¹⁺ and Ca²⁺ showed a high selectivity for UO₂ ²⁺ even though there was a high concen-tration of Na¹⁺ and Ca²⁺ in the inlet solution.     

Repeated use of a hydrophobic ligand-containing porous membrane for protein recovery

A porous hollow-fiber membrane containing a phenyl group as a hydrophobic ligand was prepared by radiation-induced graft polymerization of glycidyl methacrylate, followed by successive ring-opening reactions with phenol and water. Bovine serum albumin (BSA) was bound to the ligand during permeation of a BSA solution in phosphate buffer containing 2M (NH₄)₂SO₄ through the pores of the hollow fiber. Subsequent elution with an (NH₄)₂SO₄-free buffer exhibited an elution percentage of 82%. Repeated cycles of adsorption and elution caused the accumulation of BSA on the pore surface, resulting in a decrease in the binding capacity of BSA with increasing number of cycles. In contrast, by permeating 1 M NaOH after each elution, the binding capacity of BSA was maintained even after ten cycles. This alkaline regeneration was found to be effective in ensuring repeated use of the phenyl-group-containing porous membrane for recovery of proteins.     

Long TiO2 hollow fibers with mesoporous walls: sol-gel combined electrospun fabrication and photocatalytic properties

Long TiO2 hollow fibers with mesoporous walls have been fabricated with the sol-gel combined two-capillary spinneret electrospinning technique using a triblock copolymer (Pluronic, P123, (H(C2H5O)20(C3H7O)70 (C2H5O)20OH) as a pore-directing agent. The as-prepared hollow fibers were as long as 30 cm with an outer diameter of 0.1-4 microm and wall thickness of 60-500 nm. The diameters and wall thicknesses of the hollow fibers could be tuned by adjusting the electrospinning parameters. The fiber walls were composed of mesopores 6.7 nm in diameter as calculated from the N2 adsorption/desorption isotherm. The high-resolution TEM (HR-TEM) images exhibited that the mesopores were hexagonally aligned with a low order because of the curving of the pores. When comparing with other nanostructured TiO2 materials such as commercial TiO2 nanoparticles (P25, Degussa) and mesoporous TiO2 powders, the hollow fibers exhibited higher photocatalytic activities toward degradation of methylene blue and gaseous formaldehyde.     

Effect of solution extrusion rate on morphology and performance of polyvinylidene fluoride hollow fiber membranes using polyvinyl pyrrolidone as an additive

<正>Polyvinylidene fluoride(PVDF) hollow fiber membranes prepared from spinning solutions with different polyvinyl pyrrolidone(PVP) contents(1%and 5%) at different extrusion rates were obtained by wet/dry phase process keeping all other spinning parameters constant.In spinning these PVDF hollow fibers,dimethylacetamide(DMAc) and PVP were used as a solvent and an additive,respectively.Water was used as the inner coagulant.Dimethylformamide(DMF) and water(30/70) were used as the external coagulant.The performances of membranes were characterized in terms of water flux,solute rejection for the wet membranes.The structure and morphology of PVDF hollow fiber were examined by BET adsorption,dry/wet weight method and scanning electron microscopy(SEM).It is found that the increase in PVP content and extrusion rate of spinning solution can result in the increase of water flux and decrease of solute rejection.The improvements of interconnected porous structure and pore size are induced by shear-thinning behavior of spinning solution at high extrusion rates,which could result in the increase of water flux of hollow fiber membranes.The increase of extrusion rate also leads to the increase of membrane thickness due to the recovery effect of elastic property of polymer chains.     

SURFACE MODIFICATION OF POLYPROPYLENE MICROPOROUS MEMBRANES BY THE ADSORPTION OF NON-IONIC SURFACTANTS

Surface modification by physical adsorption of a series of non-ionic surfactants including Tween 20, Tween 40, Tween 60, Tween 80 and Tween 85, was accomplished on polypropylene microporous hollow fiber and flat membranes. The adsorption curve of the membrane surface was analyzed by weight measurements and the typical results showed a twoplatform character similarly. Differences in the degree and curve shape of adsorption resulting from such factors as concentration, temperature, as well as water cleaning time were observed for Tween 85 among other Tweens. Attenuated total reflection - Fourier transform infrared spectroscopy analysis and field emission scanning electron microscopy observation showed that the adsorption of Tween on polypropylene microporous membrane （PPMM） is effective and occurs mainly in the pores of PPMMs at low adsorption amount, and on the membrane surface also at high adsorption value.     

Preliminary Screening and Analysis of Biomembrane Permeable Compounds in Herbal Medicines: Hollow Fiber Liposome Microscreening Combined with HPLC

An advantageous method based on hollow fiber liposome microscreening (HFLMS) combined with high-performance liquid chromatography (HPLC) has been developed and used in preliminary screening and analysis of biomembrane permeable compounds from herbal medicines (HMs). In the method, a liposome hollow fiber was prepared as a screening tool; permeable compounds that could specifically bind to liposomes were screened from herbal extract to liposome in the pores and lumen of hollow fiber, then permeable compounds were dissociated from liposomes and analyzed by HPLC. The chromatographic separation was applied with a Zorbax Eclipse XDB-C18 column by a gradient elution using acetonitrile, methanol, and phosphoric acid aqueous solution as the mobile phases. In the study, influencing factors of the screened target compounds were investigated and optimized. Under optimum conditions, the surface properties of liposome hollow fibers were characterized, the nonspecific binding between the active center of hollow fiber and the bioactive components were investigated, the repeatability of this method was tested. And eight permeable compounds of flavonoids and anthraquinones from HMs were preliminarily screened and analyzed by HFLMS-HPLC. The results demonstrated that new method is a simple, fast, effective, and reliable method for preliminary screening and analyzing biomembrane permeable ingredients in HMs, and it can be used in screening other permeable compounds in HMs.

     

Preliminary Screening and Analysis of Biomembrane Permeable Compounds in Herbal Medicines: Hollow Fiber Liposome Microscreening Combined with HPLC

An advantageous method based on hollow fiber liposome microscreening (HFLMS) combined with high-performance liquid chromatography (HPLC) has been developed and used in preliminary screening and analysis of biomembrane permeable compounds from herbal medicines (HMs). In the method, a liposome hollow fiber was prepared as a screening tool; permeable compounds that could specifically bind to liposomes were screened from herbal extract to liposome in the pores and lumen of hollow fiber, then permeable compounds were dissociated from liposomes and analyzed by HPLC. The chromatographic separation was applied with a Zorbax Eclipse XDB-C18 column by a gradient elution using acetonitrile, methanol, and phosphoric acid aqueous solution as the mobile phases. In the study, influencing factors of the screened target compounds were investigated and optimized. Under optimum conditions, the surface properties of liposome hollow fibers were characterized, the nonspecific binding between the active center of hollow fiber and the bioactive components were investigated, the repeatability of this method was tested. And eight permeable compounds of flavonoids and anthraquinones from HMs were preliminarily screened and analyzed by HFLMS-HPLC. The results demonstrated that new method is a simple, fast, effective, and reliable method for preliminary screening and analyzing biomembrane permeable ingredients in HMs, and it can be used in screening other permeable compounds in HMs.     

二苯并噻吩分子印迹复合膜的制备及脱硫性能的研究

聚丙烯中空纤维膜经多巴胺氧化、硅烷化两步表面改性处理后,以甲基丙烯酸为功能单体进行表面分子印迹聚合,制备了中空纤维膜支撑-二苯并噻吩分子印迹复合膜(MIP-PP膜)。利用红外光谱、扫描电镜对印迹复合膜形态结构进行表征,测定了MIP-PP膜的脱硫性能。结果表明,在298 K时,MIP-PP膜对DBT的吸附在180 min达到平衡,最大吸附容量为133.32 mg/g;MIP-PP膜对DBT的吸附符合Lagergren准一级动力学模型及Langmuir吸附等温线,是可自发进行的放热过程。     

Oxidized single-walled carbon nanohorns as sorbent for porous hollow fiber direct immersion solid-phase microextraction for the determination of triazines in waters

This paper evaluates the potential of oxidized single-walled carbon nanohorns (o-SWNHs) immobilized on the pores of a hollow fiber (HF) for the direct immersion solid-phase microextraction of triazines from waters. The fabrication of the device requires the oxidation of the nanoparticles by means of microwave irradiation in order to obtain a homogeneous dispersion in methanol. Then, a porous hollow fiber is immersed in the methanolic dispersion of the o-SWNHs under ultrasound stirring. This procedure permits the immobilization of the o-SWNHs in the pores of the hollow fiber. For the extraction, a stainless steel wire was introduced inside the fiber to allow the vertical immersion of the o-SWNHs-HF in the aqueous standard/water sample. The triazines were preconcentrated on the immobilized o-SWNHs and further eluted using 150 μL of methanol. The solvent was evaporated and the residue reconstituted in 10 μL of methanol for sensitivity enhancement. Gas chromatography–mass spectrometry was selected as instrumental technique. The limits of detection were between 0.05 and 0.1 μg?L^?1 with an excellent precision (expressed as relative standard deviation) between runs (below 10.2 %) and between fibers (below 12.8 %). Finally, the method was applied to the determination of the triazines in fortified waters, an average recovery value of 90 % being obtained.     

High-sensitivity capillary electrophoresis for speciation of organomercury in biological samples using hollow fiber-based liquid-liquid-liquid microextraction combined with on-line preconcentration by large-volume sample stacking

A hollow fiber-based liquid-liquid-liquid microextraction (HF-LLLME) combined with on-line large-volume sample stacking (LVSS) has been developed for the speciation of organomercury in biological samples by CE with UV detection. Separation was achieved in less than 11 min with an electrolyte consisting of 35 mM sodium tetraborate at pH 9.1. In LVSS, a reverse electrode polarity-stacking mode (REPSM) was applied as on-line preconcentration strategy. In HF-LLLME, the analytes were extracted from 12 mL volume of sample solution (pH adjusted to 3.0) into bromobenzene impregnated in the pores of the hollow fiber, and into an acceptor solution of L-cysteine (15 microL, 0.02% w/v) inside the hollow fiber. Under the optimized conditions, concentration factors of 2610-4580 were achieved and LODs in the range of 0.03-0.14 microg/L were feasible. The linearity was found to be over two orders of magnitude with correlation coefficient of 0.9991-0.9996. The developed method has been validated using a certified reference material (DORM-2, dogfish muscle), and the determined values coincided very well with the certified values. The method was also applied to the speciation of organomercury in three kinds of fish samples and human hair samples.     

加电中空纤维膜萃取-离子色谱法测定乙酸丁酯中的无机阴离子

以去离子水为萃取剂,通过加电膜萃取装置萃取了乙酸丁酯中的无机阴离子.在600 V直流电压作用下,乙酸丁酯中的4种无机阴离子经中空纤维膜膜孔进入膜内的去离子水中,采用离子色谱对萃取液进行分析.最佳萃取条件为:施加电压600 V;搅拌速度600 r/min;萃取时间5 min.应用本方法测定乙酸丁酯样品,4种无机阴离子的线...     

Determination of brilliant green from fish pond water using carbon nanotube assisted pseudo-stir bar solid/liquid microextraction combined with UV-vis spectroscopy-diode array detection

This paper describes the development of a new design of hollow fiber solid/liquid phase microextraction (HF-SLPME) for determination of brilliant green (BG) residues in water fish ponds. This method consists of an aqueous donor phase and carbon nanotube reinforced organic solvent (acceptor phase) operated in direct immersion sampling mode. The multi-walled carbon nanotube dispersed in the organic solvent is held in the pores and lumen of a porous polypropylene hollow fiber. It is in contact directly with the aqueous donor phase. In this method the solid/liquid extractor phase is supported using a polypropylene hollow fiber membrane. Both ends of the hollow fiber segment are sealed with magnetic stoppers. This device is placed inside the donor solution and plays the rule of a pseudo-stir bar. It is disposable, so single use of the fiber reduces the risk of carry-over problems. Brilliant green (BG) after extraction from the aqueous samples with mentioned HF-SLPME device was determined by ultraviolet-visible spectroscopy with diode array detection (UV-vis/DAD). The absorption wavelength was set to 625 nm (λ(max)). The effect of different variables on the extraction was evaluated and optimized to enhance the sensitivity and extraction efficiency of the proposed method. The calibration curve was linear in the range of 1.00-10,000 μg L(-1) of BG in the initial solution with R(2)=0.979. Detection limit, based on three times the standard deviation of the blank, was 0.55 μg L(-1). All experiments were carried out at room temperature (25±0.5°C).     

Combination of liquid-phase microextraction and on-column stacking for trace analysis of amino alcohols by capillary electrophoresis

We described a new method for the enrichment of basic drugs present in water samples via liquid-phase microextraction (LPME) combined with on-column stacking in capillary electrophoresis. Two steps were employed to enhance the detection sensitivity of four amino alcohols. The analytes were first extracted from aqueous sample (donor solution) that were adjusted to basic through a thin layer of 1-octanol entrapped within the pores of a polypropylene hollow fiber, and then into a 5-microl acidic acceptor solution inside the hollow fiber. The extract was then further enriched through on-column stacking in capillary electrophoresis. With this two-step enrichment procedure, the method provided 72-110-fold preconcentration of the target amino alcohols. The limits of detection were 0.08-0.5 microg/ml. Relative standard deviation (n=6) ranged between 4.3 and 6.9% for the studied drugs utilizing 2-amino-1-phenylethanol as internal standard. The extraction of amino alcohols in spiked urine samples was evaluated using the developed procedure.     

中空纤维膜液相微萃取-高效液相色谱法测定醋酸氯己定痔疮栓中的醋酸氯己定

建立了中空纤维膜液相微萃取-高效液相色谱（HPLC）测定醋酸氯己定痔疮栓中醋酸氯己定含量的方法。将样品用醋酸水溶液萃取5次,配成样品溶液,然后用装有正辛醇的中空纤维膜进行液相微萃取,萃取液用高效液相色谱测定。醋酸氯己定的质量浓度为0.5 ～ 16 mg/L时与其峰面积呈良好的线性关系,加样回收率大于98.0%,相对标准偏差低于4.0%。该方法样品处理简单、快速,灵敏度与不经过液相微萃取的HPLC方法相比提高了约24倍,醋酸氯己定痔疮栓中的其他物质对测定无干扰。