Liquid-liquid-liquid microextraction for sample preparation of biological fluids prior to capillary electrophoresis.

Methamphetamine as a model compound was extracted from 2.5-mL aqueous samples adjusted to pH 13 (donor solution) through a thin phase of 1-octanol inside the pores of a polypropylene hollow fiber and finally into a 25-microL acidic acceptor solution inside the hollow fiber. Following this liquid-liquid-liquid microextraction (LLLME), the acceptor solutions were analyzed by capillary zone electrophoresis (CE). Extractions were performed in simple disposable devices each consisting of a conventional 4-mL sample vial, two needles for introduction and collection of the acceptor solution, and a 8-cm piece of a porous polypropylene hollow fiber. From 5 to 20 different samples were extracted in parallel for 45 min, providing a high sample capacity. Methamphetamine was preconcentrated by a factor of 75 from aqueous standard solutions, human urine, and human plasma utilizing 10(-1) M HCl as the acceptor phase and 10(-1) M NaOH in the donor solution. In addition to preconcentration, LLLME also served as a technique for sample cleanup since large molecules, acidic compounds, and neutral components were not extracted into the acceptor phase. Utilizing diphenhydramine hydrochloride as internal standard, repetitive extractions varied less than 5.2% RSD (n = 6), while the calibration curve for methamphetamine was linear within the range 20 ng/microL to 10 micrograms/mL (r = 0.9983). The detection limit of methamphetamine utilizing LLLME/CE was 5 ng/mL (S/N = 3) in both human urine and plasma.     

Dynamic liquid-liquid-liquid microextraction with automated movement of the acceptor phase

A new dynamic liquid-liquid-liquid microextraction procedure, with the automated movement of acceptor phase (LLLME/AMAP) to facilitate mass transfer, was developed in this study. Four compounds, 3-nitrophenol, 4-nitrophenol, 3,4-dinitrophenol, and 2,4-dichlorophenol, were used as model compounds to be preconcentrated from water samples. The extraction involved filling a 2-cm length of hollow fiber with 4 muL of acceptor solution using a conventional microsyringe, followed by impregnation of the pores of the fiber wall with 1-octanol. The fiber was then immersed in 4 mL of aqueous sample solution. The analytes in the sample solution were extracted into the organic solvent and then back-extracted into the acceptor solution. During extraction, the acceptor phase was repeatedly moved in and out of the hollow fiber channel and the syringe controlled by a syringe pump. Separation and quantitative analyses were then performed by using high-performance liquid chromatography. The results indicated that up to 400-fold enrichment of the analytes could be obtained under the optimized conditions. The enrichment factors were two times those of static liquid-liquid-liquid microextraction. Good repeatabilities (RSD values below 9.30%) were obtained. The calibration linear range was from 10 to 1000 ng/mL with the square of the correlation coefficient (r2) >0.9916. Detection limits were in the range of 0.45-0.98 ng/mL. In addition, as compared with the previously reported dynamic three-phase microextraction in which there was no relative movement between the acceptor and the organic phase (which is not conducive to effective mass transfer), this new method shows much higher extraction efficiency. All these results suggest that this new dynamic LLLME/AMAP technique could be a better alternative to the previous LLLME for the extraction of analytes from aqueous samples.     

Two-step liquid-liquid-liquid microextraction of nonsteroidal antiinflammatory drugs in wastewater

A simple and novel two-step liquid-liquid-liquid microextraction technique combined with reversed-phase HPLC has been developed for the determination of the nonsteroidal antiinflammatory drugs ibuprofen and 2-(4-chlorophenoxy)-2-methylpropionic acid in wastewater samples. In the first step, the analytes were extracted from an acidified sample (donor solution) into 1-octanol immobilized in the pores of 10 pieces of polypropylene hollow fiber and further into a basic acceptor phase inside the hollow fiber channels. This first extraction step, using 0.01 M NaOH as the acceptor phase and 0.1 M HCl within the donor phase, had a 100% relative recovery with an enrichment factor of 100-fold. The extract in the first step was then adjusted to acidic condition with HCl. It now represented the donor phase for the second step of the extraction, using a single piece of hollow fiber, with 2 microL of 0.01 M NaOH solution as the acceptor phase. This analyte-enriched acceptor phase was subsequently withdrawn into a microsyringe and directly injected into an HPLC system for analysis. With this two-step microextraction, sensitivity enhancement of >15,000-fold could be obtained. Detection limits of < or =100 ng/L could be achieved for both compounds. The method was applied to the analysis of wastewater.     

Liquid-phase microextraction combined with hollow fiber as a sample preparation technique prior to gas chromatography/mass spectrometry

Two modes of liquid-phase microextraction (LPME) combined with hollow fiber (HF) were developed for gas chromatography/mass spectrometry (GC/MS). Both methodologies, that is, static LPME with HF and dynamic LPME with HF, involved the use of a small volume of organic solvent impregnated in the hollow fiber, which was held by the needle of a conventional GC syringe. In static LPME/HF, the hollow fiber impregnated with solvent was immersed in the aqueous sample, and the extraction processed under stirring; in dynamic LPME/HF, the solvent was repeatedly withdrawn into and discharged from the hollow fiber by a syringe pump. This is believed to be the first reported instance of a semiautomated liquid microextraction procedure. The performance of the two techniques was demonstrated in the analysis of two PAH compounds in an aqueous sample. Static LPME/HF provided approximately 35-fold enrichment in 10 min and good reproducibility (approximately 4%). Dynamic LPME/HF could provide higher enrichment (approximately 75-fold) in 10 min and even better reproducibility (approximately 3%). Both methods allow the direct transfer of extracted analytes to a GC/MS system for analysis.     

Solvent bar microextraction

In this work, a new and simple microextraction method termed solvent bar microextraction (SBME) was developed. In this method, the organic extractant solvent (1-octanol) was confined within a short length of a hollow fiber membrane (sealed at both ends) that was placed in a stirred aqueous sample solution. Tumbling of the extraction device within the sample solution facilitated extraction. Pentachlorobenzene (PCB) and hexachlorobenzene (HCB) were used as model compounds to investigate the extraction performance. Analysis was carried out by gas chromatography/electron capture detection. This new method provided very high enrichment (approximately 110-fold for PCB and approximately 70-fold for HCB) in 10 min and good reproducibility (<4%, n = 6). Since the hollow fiber membrane was sealed, it could be used for extraction from "dirty" samples, such soil slurries. This novel microextraction method was compared with single-drop microextraction and static hollow fiber membrane microextraction in which the extractant solvent was also held within a hollow fiber but with the latter fixed to a syringe needle (i.e., there was no tumbling effect). Comparison between SBME and conventional solid-phase microextraction in a soil slurry sample was also investigated.     

Liquid-phase microextraction of phenolic compounds combined with on-line preconcentration by field-amplified sample injection at low pH in micellar electrokinetic chromatography.

This paper describes a novel method that applies field-amplified sample injection (FASI) in micellar electrokinetic chromatography (MEKC) with a low pH background electrolyte (BGE). Six phenolic compounds prepared in water or NaOH solution were used as the test analytes. Sample was injected electrokinetically after the introduction of a plug of water. During the injection, the water plug was pumped out of the capillary inlet by the electroosmotic flow, and the phenolic anions migrated very quickly in the direction of the outlet. When the anions reached the boundary between the water plug and BGE, they were neutralized and ceased moving. Thereafter, MEKC was initiated for the separation. This on-line preconcentration method could be conveniently coupled with a liquid-liquid-liquid microextraction procedure, in which a hollow fiber was used as an extraction solvent support to extract the analytes from the water sample. The acceptor phase consisted of 8 mM NaOH. After extraction, the extract was analyzed directly by MEKC, as described.     

Liquid-phase microextraction as an on-line preconcentration method in capillary electrophoresis

A simple and efficient sample preconcentration method for capillary electrophoresis has been developed using liquid-phase microextraction (LPME). A thin layer of an organic liquid was used to separate a drop of the aqueous acceptor phase hanging at the inlet of a capillary from the bulk aqueous donor phase. The donor-phase pH was 1.0, and the acceptor phase pH was 9.5. This pH difference caused the preconcentration of the acidic compounds, fluorescein and fluorescein isothiocyanate, into the acceptor-phase drop. Enrichment factors of 3 orders of magnitude were obtained with 30-min LPME at 35 degrees C.     

Sample preparation using a miniaturized supported liquid membrane device connected on-line to packed capillary liquid chromatography

A miniaturized supported liquid membrane device has been developed for sample preparation and connected on-line to a packed capillary liquid chromatograph. The device consists of hydrophobic polypropylene hollow fiber, inserted and fastened in a cylindrical channel in a Kel-F piece. The pores of the fiber are filled with an organic solvent, in this study 6-undecanone, thus forming a liquid membrane. The sample is pumped on the outside of the hollow fiber (donor), and the analytes are selectively enriched and trapped in the fiber lumen (acceptor). With this approach, the volume of the acceptor solution can be kept as low as 1-2 μL. This stagnant acceptor solution is then transferred through capillaries attached to the fiber ends to the LC system. The system was tested with a secondary amine (bambuterol), as a model substance in aqueous standard solutions as well as in plasma. The best extraction efficiency in aqueous solution, with an acceptor volume of 1.9 μL, was 32.5% at a donor flow rate of 2.5 μL/min. At flow rates above 20 μL/min, the concentration enrichment per time unit was approximately constant, at 0.9 times/min, i.e., 9 times enrichment in about 10 min. The overall repeatability (RSD) for spiked plasma samples was ～4% (n = 12). Linear calibration curves of peak area versus bambuterol concentration were obtained for both aqueous standard solutions and spiked plasma samples. The detection limit for bambuterol in plasma, after 10 min of extraction at a flow rate of 24 μL/min, was 80 nM.     

The XT-tube extractor: a hollow fiber-based supported liquid membrane extractor for bioanalytical sample preparation

A new supported liquid membrane extractor for bioanalytical sample preparation is presented. The extractor consists of a polypropylene hollow fiber mounted inside a PTFE tube by means of a cross-connector and a tee-connector. All parts are commercially available, inexpensive, and easily assembled. An organic solvent in the pores of the fiber forms a liquid membrane that separates the sample, which is pumped along the outside of the fiber, from the acceptor phase, which is pumped inside. The length of the hollow fiber may easily be varied to meet different demands on extractive surface and extract volumes. To test the system, the strongly acidic plasticizer/flame retardant metabolite diphenyl phosphate ester (DPhP), with a pKa value of 0.26, was extracted from urine. DPhP was protonated using 4 M hydrochloric acid and extracted into an acceptor phase at pH 9. Thirty extractions were made with the same liquid membrane without any decrease in extraction efficiency and with a relative standard deviation <7%. An analyte concentration enrichment of 5-10 times was achieved in the extraction step, giving a limit of detection (S/N = 3) of 0.014 microg/mL with LC/ESI-MS and 0.18 microg/mL with CE-UV. The effects on extraction efficiency using different sample pH, organic solvents, sample flow rates, and lengths of the fiber were evaluated.     

On-line hyphenation of capillary isoelectric focusing and capillary gel electrophoresis by a dialysis interface

An on-line two-dimensional (2D) capillary electrophoresis (CE) system consisting of capillary isoelectric focusing (CIEF) and capillary gel electrophoresis (CGE) was introduced. To validate this 2D system, a dialysis interface was developed by mounting a hollow fiber on a methacrylate resin plate to hyphenate the two CE modes. The two dimensions of capillary shared a cathode fixated into a reservoir in the methacrylate plate; thus, with three electrodes and only one high-voltage source, a 2D CE framework was successfully established. A practical 2D CIEF-CGE experiment was carried out to deal with a target protein, hemoglobin (Hb). After the Hb variants with different isoelectric points (pIs) were focused in various bands in the first-dimension capillary, they were chemically mobilized one after another and fed to the second-dimension capillary for further separation in polyacrylamide gel. During this procedure, a single CIEF band was separated into several peaks due to different molecular weights. The resulting electrophoregram is quite different from that of either CIEF or CGE; therefore, more information about the studied Hb sample can be obtained.     

Separation and determination of polycyclic aromatic hydrocarbons by solid phase microextraction/cyclodextrin-modified capillary electrophoresis

A sensitive method for the determination of polycyclic aromatic hydrocarbons (PAHs) by solid phase microextraction coupled with cyclodextrin (CD)-modified capillary electrophoresis (CE) using UV detection has been developed. A glass fiber was prepared and used for absorbing 16 EPA priority PAHs from diluted samples until equilibrium was reached. After the glass fiber was connected to a separation capillary via an adapter, the absorbed analytes were directly released into the CE buffer stream, and electrophoretic separation was effected using a 50 mM borate, pH 9.2, buffer containing 35 mM sulfobutyloxy-β-CD, 10 mM methyl-β-CD, and 4 mM α-CD. Separation was effected since neutral PAHs differentially partitioned between the neutral and charged CD phases. Under 30 kV applied potential, separation was achieved in less than 15 min with high resolution and number of theoretical plates. Pyrene as low as 8 ppb was detected, while the highest limit of detection was 75 ppb for acenaphthene. Very satisfactory reproducibility with respect to migration time and peak area was obtained for repetitions using the same separation capillary and adapter, where only the extraction fiber was discarded after each analysis.     

Anodized aluminum wire as a solid-phase microextraction fiber

The efficiency of anodized aluminum wire was investigated as a new fiber for solid-phase microextraction (SPME). Aluminum wires were anodized by direct current in a solution of sulfuric acid at room temperature and were conditioned at 300 degrees C for 30 min. These fibers were used for the extraction of some aliphatic alcohols, BTEX, and petroleum products from gaseous samples. The extracted analytes were transferred to a GC injector using an (inhouse-designed) SPME syringe that also allowed for an easy change of SPME fibers. The results obtained prove the ability of anodized aluminum wire as a new fiber for sampling of organic compounds from gaseous samples. This behavior is due most probably to the porous layer of aluminum oxide, which is formed on the metal surfaces. In this work, the optimum conditions for the preparation and conditioning of fibers and the extraction of analytes from gaseous samples were obtained. In the optimum conditions, one fiber was used in several equal analyses and the relative standard deviations were below 5% (n = 5). However, fiber-to-fiber reproducibility was 8% (n = 5). This fiber is firm, inexpensive, and durable and can be prepared simply.     

Oligomerized phospholipid bilayers as semipermanent coatings in capillary electrophoresis

Double-chained surfactants form semipermanent coatings that prevent protein adsorption in capillary electrophoresis (CE). To make such coatings more permanent, vesicles of the unsaturated phospholipid 1,2-dioleoyl-sn-glycero-3-phosphocholine were prepared and subjected to free-radical-initiated polymerization, both inside the capillary and in free solution. The latter generated oligomers of 2-5 units based on ESI-TOF MS, and formed the more stable coating in CE. Rinsing the capillary with a solution of the ex situ oligomerized DOPC suppressed EOF (0.8 x 10(-)(8) m(2)/V.s) for more than 20 h, whereas in situ oligomerized electroosmotic flow (EOF) suppressed the EOF for only 10 h. Mixtures of anionic and cationic proteins were separated under neutral pH and low ionic strength buffer with efficiencies of 480,000-930,000 plates/m and recoveries of 75-99%.     

Analytical chemistry in a drop. Solvent extraction in a microdrop

An organic microdrop (～1.3 μL) is suspended inside a flowing aqueous drop from which the analyte is extracted. The drop-in-drop system is achieved by a multitube assembly. The aqueous phase is continuously delivered to the outer drop and is aspirated away from the bottom meniscus of the drop. After the sampling/extraction period, a wash solution replaces the sample/reagent in the aqueous layer, resulting in a clear outer aqueous drop housing a colored organic drop containing the extracted material. This also results in an automatic backwash. The color intensity of the organic drop, related to the analyte concentration, is monitored by a light-emitting diode based absorbance detector. After the analytical cycle, the organic drop is removed and replaced by a new one. The performance of the system is illustrated with the determination of sodium dodecyl sulfate (a methylene blue active substance) extracted as an ion pair into chloroform. This unique microextraction system is simple and flexible, permits automated backwashing, consumes only microquantities of organic solvents, and is capable of being coupled with other analytical systems. This concept should prove valuable for preconcentration and matrix isolation in a microscale.     

Application of direct electrospray probe to analyze biological compounds and to couple to solid-phase microextraction to detect trace surfactants in aqueous solution

This work presents two novel direct electrospray probes (DEP) to generate an electrospray without using a capillary and/or syringe pump. One of the DEPs is simply a copper coil connecting to a high-voltage power supply. The sample solution is deposited on the coil by a micropipet and the electrospray is subsequently generated at the tip of the copper coil after high voltage is applied to it. Another DEP is constructed by inserting two parallel optical fibers through the copper coil. The two fibers extend one end of the copper coil by 1 cm. Electrospray is generated at the tip of the fibers through the solution predeposited on the copper coil as the high voltage is applied on the copper coil. The ES mass spectra of myoglobin in liquid or solid phases can be obtained using this DEP-MS. Coupling the DEP to a solid-phase microextraction fiber is extremely easy, and a trace amount (in ppb range) of surfactants (Triton X-100) in the aqueous solution are selectively concentrated and detected.     

Off-line solid-phase microextraction and capillary electrophoresis mass spectrometry to determine acidic pesticides in fruits

A method based on solid-phase microextraction (SPME) and capillary electrophoresis/mass spectrometry (CE/ MS) is described for determining simultaneously five acidic pesticides (o-phenylphenol, ioxynil, haloxyfop, acifluorfen, picloram) in fruits. The CE device is coupled to an electrospray interface by a commercial sheath-flow adapter. Emphasis is placed on fulfillment of the speed and sensitivity requirements. The best separation is achieved using 32 mM ammonium formate/acid formic buffer at pH 3.1, with a working voltage of 25 kV. The MS detection of the five pesticides was performed in negative ionization mode. Full-scan spectra with base peaks corresponding to [M-H]- were obtained except for acifluorfen, which gives [M-H-CO2]- as most abundant ion. Compared with the conventional EC-UV, the limits of detection were lower for acifluorfen, haloxyfop, ioxynil, and picloram, by a factor of 20, 20, 50, and 2, respectively. Extraction involved fruit sample homogenization with an acetone-water solution (5:1), filtration, and acetone evaporation prior to fiber extraction. SPME conditions such as time, pH, ion strength, stationary phase of the fiber, sample matrix, and desorption solvents were examined. The recovery of the analytes ranged from 7 to 94%, and the relative standard deviation was between 3 and, 13%. The method was found to be linear between 0.02 and 500 mg kg(-1) with correlation coefficients ranging from 0.992 to 0.997. The limits of quantification were from 0.02 to 5 mg kg(-1). The optimized method was successfully applied to the analysis of acid pesticides in fruit samples.     

Carbon film-based interdigitated array microelectrode used in capillary electrophoresis with electrochemical detection

A carbon film based interdigitated ring-shaped array (IDRA) microelectrode was applied to capillary electrophoresis with electrochemical detection to enhance the detection sensitivity on the basis of the redox cycling of electrochemical reversible species at the IDRA microelectrode. We propose a simple capillary-electrode connection device that consists of an X-Y-Z fiber aligner, an electrochemical cell, and a Nafion tubing joint that will enable the detection capillary to be aligned easily on the IDRA microelectrode and isolate the separation voltage from the electrochemical detection system. We used the off-column amperometric detection of aqueous ferrocene and catecholamines by capillary electrophoresis with an IDRA microelectrode to investigate the effects of the capillary-to-electrode distance and the separation voltage on the response currents in single and dual modes and the collection efficiencies (CE) and redox cycles (Rc) at the IDRA microelectrode. The results show that CE and Rc increase when we increase the distance and lower the separation voltage. The limiting currents also increase as the separation voltage decreases in the dual mode. Under optimum conditions, the CE and Rc of catechol, with good reversibility, reach 83.9% and 3.67, respectively. Our results showed that dual-mode detection with the IDRA microelectrode was capable of achieving lower detection limits than single-mode detection.     

Injection port derivatization following ion-pair hollow fiber-protected liquid-phase microextraction for determining acidic herbicides by gas chromatography/mass spectrometry

Injection port derivatization following ion-pair hollow fiber-protected liquid-phase microextraction (LPME) for the trace determination of acidic herbicides (2,4-dichlorobenzoic acid, 2,4-dichlorophenoxyacetic acid, 2-(2,4-dichlorophenoxy)propionic acid, 3,5-dichlorobenzoic acid, 2-(2,4,5-trichlorophenoxy)propionic acid) in aqueous samples by gas chromatography/mass spectrometry (GC/MS) was developed. Prior to GC injection port derivatization, acidic herbicides were converted into their ion-pair complexes with tetrabutylammonium chloride in aqueous samples and then extracted by 1-octanol impregnated in the hollow fiber. Upon injection, ion pairs of acidic herbicides were quantitatively derivatized to their butyl esters in the GC injection port. Thus, several parameters related to the derivatization process (i.e., injection temperature, purge-off time) were evaluated, and main parameters affecting the hollow fiber-protected LPME procedure such as extraction organic solvent, ion-pair reagent type, pH of aqueous medium, concentration of ion-pair reagent, sodium chloride concentration added to the aqueous medium, stirring speed, and extraction time profile, optimized. At the selected extraction and derivatization conditions, no matrix effects were observed. This method proved good repeatability (RSDs <12.3%, n = 6) and good linearity (r2 > or = 0.9939) for spiked deionized water samples for five analytes. The limits of detection were in the range of 0.51-13.7 ng x L(-1) (S/N =3) under GC/MS selected ion monitoring mode. The results demonstrated that injection port derivatization following ion-pair hollow fiber-protected LPME was a simple, rapid, and accurate method for the determination of trace acidic herbicides from aqueous samples. In addition, this method proved to be environmentally friendly since it completely avoided open derivatization with potentially hazardous reagents.     

Electric field-driven extraction of lipophilic anions across a carrier-mediated polymer inclusion membrane

The use of a cationic carrier-mediated polymer inclusion membrane (PIM) for extraction and preconcentration of anionic model analytes driven by an electric field directly into an aqueous acceptor solution is demonstrated. The optimized membrane was 20 μm thick and consisted of 60% cellulose triacetate as base polymer, 20% o-nitrophenyl octyl ether as plasticizer, and 20% Aliquat 336 as cationic carrier in the perchlorate form. By applying voltages of up to 700 V across the membrane, the lipophilic model analytes propanesulfonate, octanesulfonate, and decanesulfonate could be transported from the aqueous donor solution to the aqueous acceptor solution with efficiences >90% within 5 to 20 min. A preconcentration factor of 26, defined by the volume ratio between donor and acceptor compartments of the current cell design, could be achieved. The utility of the method for analytical applications is demonstrated by extraction of the herbicide glyphosate and its breakdown product aminomethylphosphonic acid from spiked river water, followed by quantification with capillary electrophoresis using contactless conductivity detection. Limits of detection of 0.8 and 1.5 ng/mL were obtained for glyphosate and aminomethylphosphonic acid, respectively.     

Analysis of n-alkanes in water samples by means of headspace solvent microextraction and gas chromatography

A simple and efficient headspace solvent microextraction (HSME) was developed for the simultaneous determination of the trace concentrations of some n-alkanes in water samples. Therefore, a microdrop of an organic solvent was extruded from the needle tip of a gas chromatographic syringe to the headspace above the surface of the solution in a sealed vial. Then the volatile organic compounds are extracted and concentrated in the microdrop. Next, the microdrop was retracted into the microsyringe and injected directly into the gas chromatograph. Experimental parameters which control the performance of HSME such as the type of microextraction solvent, organic drop and sample volume, sample stirring rate, sample solution and microsyringe needle temperatures, salt addition and exposure time profiles were investigated and optimized. Finally, the enrichment factor, dynamic linear range (DLR), limit of detection (LOD) and precision of the method were evaluated. Using optimum extraction conditions, good linearity with correlation coefficients in the range of 0.995相似文献