Liquid-phase microextraction of hydrophilic drugs by carrier-mediated transport

Basic studies on carrier-mediated transport as a mechanism to extract polar drugs by hollow fibre-based liquid-phase microextraction are presented for the first time. Hydrophilic alkaline drugs with log P (octanol/water partition coefficient) values less than 1 were selected as model substances. Sodium octanoate served as carrier and was added to the sample solution at pH 7 to form hydrophobic ion-pair complexes with the analytes. The ion-pair complexes were extracted into octanol as liquid membrane immobilised in the pores of the hollow fibre. Further extraction into an aqueous acceptor phase inside the lumen of the hollow fibre was facilitated by counter transport of protons from the acceptor solution to the sample solution. Protons from the acceptor solution released the analytes at the liquid membrane-acceptor interface and neutralized the carrier. The acceptor phase was analysed by capillary electrophoresis. The studies show that high extraction recoveries of ionic hydrophilic drugs can be obtained at a sample-acceptor volume ratio of 10. Linear calibration graphs and clean electropherograms indicate that carrier-mediated transport is a promising technique in microextraction of polar drugs from biological matrices.     

Ferrofluid-based liquid-phase microextraction

A new mode of liquid-phase microextraction based on a ferrofluid has been developed. The ferrofluid was composed of silica-coated magnetic particles and 1-octanol as the extractant solvent. The 1-octanol was firmly confined within the silica-coated particles, preventing it from being lost during extraction. Sixteen polycyclic aromatic hydrocarbons (PAHs) were used as model compounds in the development and evaluation of the extraction procedure in combination with gas chromatography-mass spectrometry. Parameters affecting the extraction efficiency were investigated in detail. The optimal conditions were as follows: 20mL sample volume, 10mg of the silica-coated magnetic particles (28mg of ferrofluid), agitation at 20Hz, 20min extraction time, and 2min by sonication with 100μL acetonitrile as the final extraction solvent. Under optimal extraction conditions, enrichment factors ranging from 102- to 173-fold were obtained for the analytes. The limits of detection and the limits of quantification were in the range of 16.8 and 56.7pgmL(-1) and 0.06 and 0.19ngmL(-1), respectively. The linearities were between 0.5-100 and 1-100ngmL(-1) for different PAHs. As the ferrofluid can respond to and be attracted by a magnet, the extraction can be easily achieved by reciprocating movement of an external magnet that served to agitate the sample. No other devices were needed in this new approach of extraction. This new technique is affordable, efficient and convenient for microextraction, and offers portability for potential onsite extraction.     

Chemical reactions in liquid-phase microextraction

In recent years, liquid-phase microextraction (LPME), a microscale implementation of liquid-liquid extraction, has become a very popular sample pretreatment technique because it combines extraction and enrichment, and is inexpensive, easy to operate and nearly solvent-free. Especially so in hollow fiber-protected LPME, sample cleanup is also effected. Essentially, owing to its high sample-to-extracting solvent volume ratio, LPME can achieve high analyte enrichment. Since its advent, the technique has been widely used, and applied to environmental, pharmaceutical, biological and forensic analyses. This review focuses on developments relating to chemical reactions associated with LPME applications, in contrast to conventional, straightforward extractions in which analytes remain as they are during the extraction process. Chemical reactions brought about during LPME serve to promote the extractability of the analytes (thus expanding the scope of applicability of the technique), facilitate their (analyte) compatibility with the analytical system and/or improve detection sensitivity. The reactions that are usually enabled during LPME include ion-pair extraction (carrier-mediated membrane transport), complexation, chemical (pre-extraction, in situ, and post-extraction) derivatization, phase-transfer catalysis and other "special affinity" reactions. Strategies on chemical reactions in LPME are overviewed in this report.     

Simultaneous determination of multi-class antibiotic residues in water using carrier-mediated hollow-fiber liquid-phase microextraction coupled with ultra-high performance liquid chromatography tandem mass spectrometry

A method has been developed for carrier-mediated hollow-fiber liquid-phase microextraction (HF-LPME) and enrichment of multiple classes of antibiotics in water samples. Eleven compounds (erythromycin, spiramycin, tilmicosin, sulfathiazole, sulfamethazine, sulfamerazine, oxytetracycline, tetracycline, ciprofloxacin, danofloxacin and enrofloxacin) from four important classes of antibiotics (of the macrolide, sulfonamide, tetracycline and quinolone type) have been simultaneously preconcentrated with one set of HF-LPME conditions, followed by determination by ultra-HPLC combined with electrospray ionization tandem mass spectrometry (UHPLC-MS/MS). Antibiotics can be determined at ng L^?1 levels using this highly sensitive and selective method. Parameters including immersion time, liquid membrane composition, sample pH, acceptor composition and extraction time were optimized to finally give detection limits in the 10?C250?ng?L^?1 range. Good linearity was achieved, with up to 156 times enrichment over the four classes of antibiotics. This multi-residue method enabled the simultaneous enrichment of all 11 multi-class antibiotics from spiked river water samples, with relative recovery between 79 and 118%.

Solid drop based liquid-phase microextraction

Solid drop based liquid-phase microextraction (SDLPME) is a novel sample preparation technique possessing obvious advantages of simple operation with a high pre-concentration factor, low cost and low consumption of organic solvent. SDLPME coupled with gas chromatography (GC), high-performance liquid chromatography (HPLC), and atomic absorption spectrometry (AAS) has been widely applied to the analyses of a different variety of samples. The basic principles, parameters affecting the extraction efficiency, and the latest applications of SDLPME are reviewed in this article.     

In-line coupling headspace liquid-phase microextraction with capillary electrophoresis

An analytical technique of in-line coupling headspace liquid-phase microextraction (HS-LPME) with capillary electrophoresis (CE) was proposed to determine volatile analytes. A special cover unit of the sample vial was adopted in the coupling method. To evaluate the proposed method, phenols were used as model analytes. The parameters affecting the extraction efficiency were investigated, including the configuration of acceptor phase, kind and concentration of acceptor solution, extraction temperature and time, salt-out effect, sample volume, etc. The optimal enrichment factors of HS-LPME were obtained with the sample volume of about half of sample vials, which were confirmed by both the theoretical prediction and experimental results. The enrichment factors were obtained from 520 to 1270. The limits of detection (LODs, S/N = 3) were in the range from 0.5 to 1 ng/mL each phenol. The recoveries were from 87.2% to 92.7% and the relative standard deviations (RSDs) were lower than 5.7% (n = 6). The proposed method was successfully applied to the quantitative analysis of the phenols in tap water, and proved to be a simple, convenient and reliable sample preconcentration and determination method for volatile analytes in water samples.     

Dynamic headspace time-extended helix liquid-phase microextraction

Liquid-phase microextraction (LPME) has been proved to be a fast, inexpensive and effective sample pre-treatment technique for the analyses of pesticides and many other compounds. In this investigation, a new headspace microextraction technique, dynamic headspace time-extended helix liquid-phase microextraction (DHS-TEH-LPME), is presented. In this work, use of a solvent cooling system, permits the temperature of the extraction solvent to be lowered. Lowering the temperature of the extraction solvent not only reduces solvent loss but also extends the feasible extraction time, thereby improving extraction efficiency. Use of a larger volume of the solvent not only extends the feasible extraction time but also, after extraction, leaves a larger volume to be directly injected into the gas chromatography (GC) to increase extraction efficiency and instrument signal. The DHS-TEH-LPME technique was used to extract six organochlorine pesticides (OCPs) from 110 ml water samples that had been spiked with the analytes at ng/l levels, and stirred for 60 min. The proposed method attained enrichments up to 2121 fold. The effects of extraction solvent identity, sample agitation, extraction time, extraction temperature, and salt concentration on extraction performance were also investigated. The method detection limits (MDLs) varied from 0.2 to 25 ng/l. The calibration curves were linear for at least 2 orders of magnitude with R² ≧ 0.996. Relative recoveries in river water were more than 86%.     

Dynamic hollow fiber-supported headspace liquid-phase microextraction

With the increasing concern over deteriorating environmental quality, the analysis of organic pollutants in air, water, and soil has become critically important. The development of simple, efficient, and inexpensive analytical sample pretreatment is crucial for monitoring and evaluating the environment. In this work, a dynamic hollow-fiber supported headspace liquid-phase microextraction (DHF-HS-LPME) approach was developed. In dynamic LPME, the extracting solvent is held within a hollow fiber, affixed to a syringe needle and immersed in the sample solution, and is moved to-and-fro by using a programmable syringe pump. The movement facilitates mass transfer from the sample to the solvent. Here, a similar approach was adopted, except that extraction was from the headspace rather than by direct immersion. Analysis of the extract was carried out by gas chromatography-mass spectrometry. The effect of sampling temperature, water, salt, dwelling time were investigated. Results indicated that this novel headspace microextraction method gave good analyte-enrichment factors, linear range, limits of detection and repeatability, all of which were evaluated by extracting PAHs from soil samples. This technique represents an inexpensive, convenient, fast and simple sample preparation of this class of semi-volatile organic compounds.     

Dynamic headspace liquid-phase microextraction of alcohols

A method was developed using dynamic headspace liquid-phase microextraction and gas chromatography-mass spectrometry for extraction and determination of 9 alcohols from water samples. Four different solvents, hexyl acetate, n-octanol, o-xylene and n-decane were studied as extractants. The analytes were extracted using 0.8 microl of n-octanol from the headspace of a 2 ml sample solution. The effect of sampling volume, solvent volume, sample temperature, syringe plunger withdrawal rate and ionic strength of the solution on the extraction performance were studied. A semiautomated system including a variable speed stirring motor was used to ensure a uniform movement of syringe plunger through the barrel. The method provided a fairly good precision for all compounds (5.5-9.3%), except methanol (16.4%). Detection limits were found to be between 1 and 97 microg/l within an extraction time of approximately 9.5 min under GC-MS in full scan mode.     

Electrochemical coupling in carrier-mediated membrane transport

The possibility of controlling permeant flux through facilitated-transport membranes by passage of electric current is examined theoretically. The major effects observed are due to the role of the electrodes as sources and sinks for the species which participate in the electrode reactions. If those species also participate in the homogeneous chemical reactions, the passage of current can profoundly influence the membrane permeability. Order of magnitude increases in permeant flux are predicted, as is the pumping of permeant against its overall concentration difference. Predicted energy consumption is competitive with that of conventional separation processes.     

Electrical pumping in carrier-mediated membrane transport

A model of carrier-mediated pumping induced by electrochemical (redox) reactions is presented. The model is compared with published data for the facilitated transport of nitric oxide in a formamide membrane containing dissolved ferrous and ferric chlorides wherein the flux of nitric oxide is augmented by diffusion of the reversible complex, (NO—Fe²⁺. Passing a current through the membrane drives the reduction of ferric ions at the cathode and the oxidation of ferrous ions at the anode, coupling the charge and mass fluxes within the membrane. Our results indicate that this electrically powered, carrier-mediated membrane can pump permeant up to a concentration 0(10) times greater than that in the feed.     

Analysis of quinolones by voltage-assisted liquid-phase microextraction combined with LC-MS

The method of liquid-phase microextraction assisted with voltage was developed and applied on determination of quinolones in water sample in this study. Both of the reproducibility and extraction time were improved with the aid of applying voltage. Four analytes in neutral state such as cinoxacin, oxolinic acid, nalidixic acid, and flumequine were extracted from a sample solution at pH 2.0, through a polypropylene hollow fiber which was immobilized with 2-octanone, and then into a 25 μL of the acceptor phase of 40 mM borate buffer at pH 10.0 by applying voltage of 100 V. Subsequently, the acceptor solution was directly subjected to analysis by LC-MS. The performance of the method for four quinolones was also evaluated. Linearity was obtained in the range of 1.0-25.0 ng/mL with R(2) > 0.996. Limits of detection were below 0.6 ng/mL, and recoveries of water sample were ranged from 90.8 to 109.6%.     

Advances in sample preparation using membrane-based liquid-phase microextraction techniques

The article highlights some of the most important developments in membrane-based liquid-phase microextraction techniques and applications. We discuss the evolution of different configurations from the flat type of module through the hollow-fiber module to the latest membrane combination with other sorbents and coating of the hollow fiber. We also discuss the basic principles and important parameters that control the extraction process in two-phase and three-phase systems. Finally, we highlight future trends in module configuration and applications.     

Temperature-controlled headspace liquid-phase microextraction device using volatile solvents

A novel temperature-controlled headspace liquid-phase microextraction (TC-HS-LPME) device was established in which volatile solvents could be used as extractant. In this device, a PTFE vial cap with a cylindrical cavity was used as the holder of the extraction solvent. Up to 40 μl of extraction solvent could be suspended in the cavity over the headspace of aqueous sample in the vial. A cooling system based on thermoelectric cooler (TEC) was used to lower the temperature of extractant in PTFE vial cap to reduce the loss of volatile solvent during extraction process and increase the extraction efficiency. The selection of solvents for HS-LPME was then extended to volatile solvents, such as dichloromethane, ethyl acetate and acetone. The use of volatile extraction solvents instead of semi-volatile solvent reduced the interference of the large solvent peak to the analytes peaks, and enhanced the compatibility of HS-LPME with gas chromatograph (GC). Moreover, the use of larger volume of extractant solvent increases the extraction capacity and the injection volume of GC after extraction, thus improving detection limits. Several critical parameters of this technique were investigated by using chlorobenzenes (CBs) as the model analytes. High enrichment factors (498–915), low limits of detection (0.004–0.008 μg/L) and precision (3.93–5.27%) were obtained by using TC-HS-LPME/GC-FID. Relative recoveries for real samples were more than 83%.     

Sensitive analysis of amino acids with carrier-mediated single drop microextraction in-line coupled with capillary electrophoresis

In order to analyze amino acids sensitively without derivatization, we have developed carrier-mediated single drop microextraction (SDME). Nonane-1-sulfonic acid was added to an acidic sample donor solution as a carrier to form neutral ion pair complexes with amino acids. The ion pair complexes were extracted to the organic phase, covering a drop of an aqueous basic acceptor phase hanging at the tip of a capillary, and then back-extracted to the basic acceptor phase, where both the amino acids and the carrier have negative charges and the ion pair complexes are broken. The resulting extract of enriched amino acids was injected into the capillary and analyzed by capillary electrophoresis. With 20-min SDME with agitation of the donor phase, enrichment factors of four aromatic amino acids were up to 120-fold, yielding the LOD of 70-500 nM. The linear dynamic ranges for corrected peak areas were 1-100 μM with linear correlation coefficients larger than 0.9959. With internal standardization, the intraday RSDs of migration times and corrected peak areas were 0.01-0.04% and 2.0-3.7%, respectively. The capabilities of sample cleanup including desalting and preconcentration of carrier-mediated SDME were demonstrated with the analysis of human urine after minimal pretreatment of acidification and centrifugation.     

Determination of phenolic compounds in wastewater by liquid-phase microextraction coupled with gas chromatography

Liquid-phase microextraction (LPME) coupled with gas chromatography-flame ionization detection is applied to the analysis of phenolic compounds (phenol, o-cresol, m-cresol, 2,4-dimethylphenol, 2,3- dimethylphenol, and 3,4-dimethylphenol) in water samples. Experimental parameters affecting the extraction efficiency (including extraction solvent and drop volume, stirring rate, extraction time, temperature, salt concentration, and pH) are investigated and optimized. The developed protocol yields a good linear calibration curve from 5 or 20 to 10000 microg/L for the target analytes. The limits of detection are in the range of 0.94 to 1.97 microg/L, and the relative standard deviation is below 9.37%. The established method is applied to determine the phenolic pollutants in real wastewater samples from a coking plant. The recoveries of the phenolic compounds studied are from 92% to 102%, suggesting the feasibility of the LPME method for the determination of the phenolic compounds in wastewater.     

Dynamic liquid-phase microextraction with HPLC for the determination of phoxim in water samples

A new method, which involves dynamic liquid-phase microextraction followed by HPLC with variable wavelength detection, was developed to determine phoxim in water samples. Experimental parameters affecting the extraction efficiency, such as extraction solvent, solvent volume, sampling volume, dwell time, number of samplings, and salt concentration were investigated. Under the optimal extraction conditions, phoxim was found to yield a good linear calibration curve in the concentration range from 0.01 to 10 microg/mL. The LOD is 2 ng/mL, and RSD at the 100 ng/mL levels is 8.9%. Lake water and tap water samples were successfully analyzed using the proposed method.     

顶空液相微萃取测定溶剂型涂料中挥发性有机物

应用顶空液相微萃取法对溶剂型涂料中的挥发性有机物(VOC)进行分离富集,直接进样气相色谱法分析。对萃取溶剂进行了筛选,并研究了平衡温度、溶剂体积、萃取时间等影响因素对萃取效率的影响。在优化的条件下,苯、甲苯、二甲苯、三氯乙烯和四氯乙烯的检出限分别为0.25、0.25、0.75、1.25和1.75μg/L。进行了方法的准确度和精密度试验,平均回收率为94.14%~119.33%,相对标准偏差为2.9%~18.9%。     

Importance of extracting solvent vapor pressure in headspace liquid-phase microextraction

Of the many parameters that affect the enrichment factors in headspace liquid-phase microextraction, in this study, we systematically investigated the influence of the vapor pressure of the extracting solvent. Seven extracting solvents with different vapor pressures were selected and tested. It was found that the vapor pressure of the extracting solvent dramatically affects the enrichment factor and the factor was increasing by decreasing the extracting solvent vapor pressure under given experimental conditions. The result was validated for volatile organic compounds such as polynuclear aromatic hydrocarbons, organochlorine pesticides and polychlorinated biphenyls.