Selective extraction of triazine herbicides from food samples based on a combination of a liquid membrane and molecularly imprinted polymers

A selective extraction technique based on the combination of liquid membrane (microporous membrane liquid–liquid extraction) and molecularly imprinted polymers (MIP) was applied to triazines herbicides in food samples. Simazine, atrazine and propazine were extracted from aqueous food samples through the hydrophobic porous membrane that was impregnated with toluene, which also formed part of the acceptor phase. In the acceptor phase, the compounds were re-extracted onto MIP particles. The extraction technique was optimised for the amount of molecularly imprinted polymers particles in the organic acceptor phase, extraction time, and type of organic acceptor solvent and desorption solvent. An extraction time of 90 min and 50 mg of MIP were found to be optimum parameters. Toluene as the acceptor phase was found to give higher triazines binding onto MIP particles compared to hexane and combinations of diethyl ether and hexane. 90% methanol in water was found to be the best desorption solvent compared to acetonitrile, methanol and water. The selectivity of the technique was demonstrated by extracting spiked lettuce and apple extracts where clean chromatograms were obtained compared to liquid membrane extraction alone or to the microporous membrane liquid–liquid extraction – non-imprinted polymer combination. The MIP showed a certain degree of group specificity and the extraction efficiency in lettuce extract was 79% (0.72) for simazine, 98% (1.55) for atrazine and 86% (3.08) for propazine.     

Selective extraction of triazine herbicides based on a combination of membrane assisted solvent extraction and molecularly imprinted solid phase extraction

A selective extraction technique based on the combination of membrane assisted solvent extraction and molecularly imprinted solid phase extraction for triazine herbicides in food samples was developed. Simazine, atrazine, prometon, terbumeton, terbuthylazine and prometryn were extracted from aqueous food samples into a hydrophobic polypropylene membrane bag containing 1000μL of toluene as the acceptor phase along with 100mg of MIP particles. In the acceptor phase, the compounds were re-extracted onto MIP particles. The extraction technique was optimised for the type of organic acceptor solvent, amount of molecularly imprinted polymers particles in the organic acceptor phase, extraction time and addition of salt. Toluene as the acceptor phase was found to give higher triazine binding onto MIP particles compared to hexane and cyclohexane. Extraction time of 120min and 100mg of MIP were found to be optimum parameters. Addition of salt increased the extraction efficiency for more polar triazines. The selectivity of the technique was demonstrated by extracting spiked cow pea and corn extracts where clean chromatograms were obtained compared to only membrane assisted solvent extraction or only molecularly imprinted solid phase extraction. The study revealed that this combination may be a simple way of selectively extracting compounds in complex samples.     

Preparation,evaluation and characterization of quercetin-molecularly imprinted polymer for preconcentration and clean-up of catechins

Molecularly imprinted polymer (MIP) for solid extraction and preconcentration of catechins have been successfully prepared by a thermal polymerization method using quercetin as template, 4-vinylpyridine as functional monomer and ethylene glycol dimethacrylate as crosslinker. A solution mixture of acetone and acetonitrile was used as porogen. Systematic investigations of the influence of monomer, cross-linker, porogen, as well as polymerization conditions on the properties of the MIPs were carried out. The quercetin MIPs were evaluated according to their selective recognition properties for quercetin, structurally related compounds (catechin, epigallocatechin gallate and epicatechin) and a unrelated compound of similar molecular size (α-tocopherol). Good binding was observed for quercetin, catechin and epigallocatechin gallate with an optimized MIP in a solid phase extraction system. Adsorption and kinetic characteristics were evaluated for catechins which indicated that the synthesized polymer had high adsorption capacity and contained homogeneous binding sites. Chemical and morphological characterization of the MIP was investigated by FTIR, SEM and BET, which confirmed a high degree of polymerization. Finally, the MIP was successfully applied to the clean-up and preconcentration of catechins from several natural samples.     

Determination of inorganic anions in ethyl acetate by ion chromatography with an electromembrane extraction method

In this work, the determination of inorganic anions in slightly water-soluble organic solvents (ethyl acetate) was realized by ion chromatography (IC) with a novel-efficient electromembrane extraction method. From an 8 mL ethyl acetate sample, three inorganic anions migrated through the pores of a polypropylene hollow fiber membrane, and into deionized water inside the lumen of the hollow fiber by the application of 600 V. The transport was forced by an electrical potential difference sustained over the liquid membrane, resulting in electrokinetic migration of inorganic anions from the donor compartment to the acceptor solution. After the electromembrane extraction, the acceptor solution was analyzed by IC with a sodium carbonate-sodium bicarbonate eluent. The applied voltage, stirring speed, and extraction time for controlling the extraction efficiency were optimized. Within 10 min of operation at 600 V, chloride, bromide, and sulfate were extracted with recoveries in the range 76-110%, which corresponded to a linear range of 0.01-1 mg/L. The procedure was applied to the analysis of inorganic anions in a real ethyl acetate sample and expands onto other slightly water-soluble organic solvents.     

Monodispersed, molecularly imprinted polymers for cinchonidine by precipitation polymerization

Three monodispersed, molecularly imprinted polymers (MIPs) for cinchonidine (CD) have been synthesized by precipitation polymerization. MIP1 was prepared using methacrylic acid (MAA) as a functional monomer and divinylbenzene (DVB) as a cross-linker and MIP2 was prepared with further addition of 2-hydroxyethyl methacrylate (HEMA) as a co-monomer. For the preparation of MIP3, core-shell type MIP, monodispersed DVB homopolymers, which are prepared by precipitation polymerization, were used as a core and CD-imprinted MAA-DVB copolymer phases were coated onto the core. Three MIPs synthesized gave monodispersed, spherical beads in micrometer sizes. The binding characteristics and molecular recognition properties of MIP1-3 were examined by Scatchard analysis and chromatographic studies. The association constant of CD with MIP1 was the highest among MIPs prepared, while that with MIP3 was the lowest. The template molecule, CD, was more retained than its stereoisomer, cinchonine, on the three MIPs, and the stereoseparation factor of 38 was obtained with MIP3.     

Modeling gradient elution in countercurrent chromatography: efficient separation of tanshinones from Salvia miltiorrhiza Bunge

Countercurrent chromatography (CCC) is a support-free liquid-liquid chromatography using centrifugal fields to hold the liquid stationary phase. CCC has been widely applied in the separation of various natural and synthetic components using a variety of biphasic liquid systems. The related hexane or heptane/ethyl acetate/methanol or ethanol/water biphasic liquid systems demonstrated their significance in CCC. Gradient is difficult in CCC since any composition change in one phase induces a composition change of the other phase to maintain phase equilibrium. This work provides a new insight into linear gradient elution in CCC that is feasible with some biphasic liquid systems such as selected compositions of the hexane/ethyl acetate/ethanol/water systems. The equations modeling solute motion inside the CCC column are proposed. Particular compositions of the liquid system, namely the hexane/ethyl acetate/ethanol/water 8:2:E:W compositions with E + W = 10, were studied from W = 1 to 9. They showed moderate changes in the upper organic phase compositions. The model is tested with the separation of tanshinones from the rhizome of Salvia miltiorrhiza Bunge. Different linear solvent gradient profiles were experimentally performed between 8:2:5:5 and 8:2:3:7 compositions and the results were evaluated using the proposed model. Five tanshinones including dihydrotanshinone I, cryptotanshinone, tanshinone I, 1,2-dihydrotanshinquinone, and tanshinone IIA have been successfully separated (>95% purities) using a gradient profile optimized by the developed model. The gradient model can be used only with biphasic liquid systems in which one phase shows minimum composition changes when the other phase composition changes notably. This case is not the general case for biphasic liquid systems but can be applied with specific compositions of the quaternary hexane or heptane/ethyl acetate/methanol or ethanol/water most useful CCC liquid systems.     

Fractionation of apple procyanidins according to their degree of polymerization by normal-phase high-performance liquid chromatography

A new method was developed for the fractionation of procyanidin oligomers according to their degree of polymerization. Monomeric flavan-3-ols and low molecular mass procyanidins were selectively extracted from the lyophilized powder of apple condensed tannins (ACTs) by methyl acetate extraction. Sequentially, the separation of each oligomer from dimer to pentamer in this extract was carried out by normal-phase high-performance liquid chromatography using a silica-beads packed column. The best separation was achieved with a mobile phase system containing hexane; (1) hexane–methanol–ethyl acetate, (2) hexane–acetone. These sequential treatments can be easily adapted to large-scale fractionation.     

Grafting of molecularly imprinted polymers from the surface of silica gel particles via reversible addition-fragmentation chain transfer polymerization: A selective sorbent for theophylline

Molecularly imprinted polymers (MIPs) were grafted successfully from the surface of silica gel particles via surface initiated reversible addition-fragmentation chain transfer (RAFT) polymerization using RAFT agent functionalized silica gel as the chain transfer agent. The intrinsic characteristics of the controlled/living polymerization mechanism of RAFT allowed for the effective control of the grafting process. Thus the grafting copolymerization of methacrylic acid and divinyl benzene in the presence of template theophylline led to thin MIP film coating silica gel (MIP-Silica). The thickness of MIP film prepared in this study is about 1.98 nm, which was calculated from the nitrogen sorption analysis results. Measured binding kinetics for theophylline to the MIP-Silica and MIPs prepared by conventional bulk polymerization demonstrated that MIP-Silica had improved mass-transfer properties. In addition, the theophylline-imprinted MIP-Silica was used as the sorbent in solid-phase extraction to determine theophylline in blood serum with satisfactory recovery higher than 90%. Nonspecific adsorption of interfering compounds can be eliminated by a simple elution with acetonitrile, without sacrificing the selective binding of theophylline.     

Extraction of glyphosate by a supported liquid membrane technique

The possible application of the supported liquid membrane (SLM) technique for the extraction of glyphosate is presented. For the extraction of this compound the SLM system has been applied with utilisation of Aliquat 336 as a cationic carrier incorporated into the membrane phase. The extraction efficiency of glyphosate [N-(phosphonomethyl)glycine] is dependent on the donor phase pH, carrier concentration in the organic phase and NaCl concentration in the acceptor phase. The optimal extraction conditions are: donor phase pH>11, acceptor phase of 2 M NaCl solution and the organic phase composed of 20% (w/w) Aliquot 336 solution in di-hexyl ether. Counter-coupled transport of chloride anions from the acceptor phase to the donor phase is a driving force of the mass transfer in this system.     

Selective 17‐β‐estradiol molecular imprinting

An efficient novel method for the synthesis of a covalent molecularly imprinted polymer (MIP) highly specific to β‐estradiol have been developed. MIP prepared by both covalent and non covalent techniques, demonstrated high selectivity toward β‐estradiol. MIPs were synthesized by radical polymerization of 17‐β‐estradiol 4‐vinyl‐benzene carboxyl or sulfonyl esters used as covalent functional monomers, methacrylic acid as noncovalent functional monomer, ethylene glycol dimethacrylate as crosslinking agent, and acetonitrile as swelling and porogenic component. Almost 35% (w/w) of 17‐β‐estradiol was successfully removed from the polymer network by basic hydrolysis. The binding ability of MIP was 10.73 μg/mg MIP following removal of 17‐β‐estradiol in the 2 mg/mL β‐estradiol solution. Selective rebinding of β‐estradiol toward MIP was tested in the presence of competitive binders including estrone, 19‐nortestosterone, epiandrosterone, and cholesterol. Estrone having closest similar chemical structure to β‐estradiol exhibited only 0.6 μg/mg MIP competitive binding, being exposed to equivalent concentrations. Moreover, other competitive steroids demonstrated negligible affinity toward MIP indicating high selectivity of novel MIP system toward β‐estradiol. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5534–5542, 2009     

2-异戊基环戊酮虚拟模板印迹微球的制备及其吸附性能

以2-异戊基环戊酮为虚拟模板,采用沉淀聚合法制备了粒径20~50 μm的分子印迹微球。 用傅里叶变换红外光谱(FTIR)和扫描电子显微镜(SEM)研究了分子印迹微球的表面化学特征及粒径分布,测试了印迹聚合物对玫瑰醚的吸附动力学、等温吸附性能及吸附选择性。 考察了分子印迹固相萃取玫瑰醚的应用效能。 结果表明:分子印迹聚合物(MIPs)对玫瑰醚的吸附可在25 min达到平衡,具有较快的吸附动力学,一级动力学模型更适合描述其吸附动力学行为。 Freundlich模型最适合描述MIPs对玫瑰醚的等温吸附行为,聚合物材料最大的印迹位点数目为149.3 μmol/g。 聚合物对玫瑰醚的平均吸附能为166 kJ/mol,表明主要为化学吸附。 虚拟模板印迹聚合物对玫瑰醚的选择因子相对于香叶醇和香茅醇分别为3.710和5.636,且对含玫瑰醚的混合物中的目标化合物仍具有较高的选择吸附能力(竞争吸附量为18.02 mg/g)。 在优化洗涤(1 mL乙腈+1 mL乙腈和水混合溶剂(体积比9.5:0.5)+2 mL乙腈、甲醇和水混合溶剂(体积比8:1:2)和洗脱(3 mL甲醇和醋酸混合溶剂(体积比9:1))条件下,通过分子印迹固相萃取可实现玫瑰醚的有效分离和富集,回收率为96.23%。     

Enantioseparation of 3‐phenyllactic acid by chiral ligand exchange countercurrent chromatography

3‐Phenyllactic acid is an antimicrobial compound with broad‐spectrum activity against various bacteria and fungus. The observed difference in pharmacological activity between optical isomeric 3‐phenyllactic acid necessitates a method for enantioseparation. Chiral ligand exchange countercurrent chromatography was investigated for the enantioseparation of 3‐phenyllactic acid with a synthesized chiral ligand. A two‐phase solvent system was composed of n‐butanol/hexane/water (0.4:0.6:1, v/v/v) to which N‐n‐dodecyl‐l ‐hydroxyproline was added to the organic phase as chiral ligand and cupric acetate was added in the aqueous phase as a transitional metal ion. The influence factors were optimized by enantioselective liquid–liquid extraction. Baseline enantioseparation of racemic 3‐phenyllactic acid by analytical high‐speed countercurrent chromatography was achieved. The optical purities of enantiomeric 3‐phenyllactic acid reached 99.0%, as determined by chiral high‐performance liquid chromatography.     

液晶分子印迹整体柱的制备及其分子识别热力学

液晶分子印迹聚合物(MIPs)因刚性液晶单体的加入而在超低交联度水平下也能印迹和识别模板分子,有效解决了传统MIPs因高交联度造成的位点包埋、结合容量低、传质慢等问题。尽管液晶MIPs具有如此独特的优势,但却面临着由于交联度的大幅度降低而导致印迹效果下降的问题。为了研究液晶MIPs的结合特性,制备具有良好印迹效果的低交联液晶MIPs,该文通过二次接枝聚合,制备了一系列不同交联度的液晶分子印迹整体柱,用高效液相色谱法研究了聚合参数与印迹整体柱亲和性的关系。实验中选用三羟甲基丙烷三甲基丙烯酸酯(TRIM)为交联剂,以甲苯和十二醇为致孔剂合成整体柱骨架,并在此基础上以(S)-萘普生为模板,加入液晶单体4-氰基苯基单环己基乙烯(CPCE)进行二次聚合接枝。实验中系统考察了流动相中乙腈比例及缓冲液pH值对色谱保留的影响,结果发现液晶单体的加入使得MIPs对萘普生保留控制机制由原来的氢键作用变为了疏水作用;通过动态吸附实验得到的突破曲线经前沿分析及对吸附等温线Langmuir、Freundlich和Scatchard分析拟合,发现交联度为15%时液晶MIPs印迹因子最大(3.78)、非均一性最强,且特异性吸附量高于非特异性吸附量。液晶MIPs的计量置换模型(SDM-R)分析表明,液晶印迹整体柱对模板分子的总亲和力(ln A=0.645)明显高于其类似物;而从空间匹配程度看,与液晶印迹整体柱空间匹配程度最高的是酮洛芬而非模板分子,但液晶印迹整体柱对酮洛芬的总亲和力(ln A=0.242)不及模板分子的一半,表明在本低交联液晶印迹系统中,空间效应不是决定印迹系统识别能力的主要因素。进一步的分离热力学研究发现,低交联液晶印迹柱的|ΔΔH|<T|ΔΔS|,而交联度为70%的非液晶MIPs柱的|ΔΔH|>T|ΔΔS|,表明液晶MIPs的分离过程是一个熵控制过程,而常规无液晶MIPs的分离过程是一个焓控制过程。上述结果表明,液晶单体的加入改变了MIPs的识别机制,适当的低交联度可显著提高液晶MIPs的识别性能,因此液晶MIPs这些特质有望使其成为新一代的MIPs。     

咖啡因分子印迹固相萃取柱的制备及应用

以咖啡因作为模板分子,α-甲基丙烯酸为功能单体,乙二醇二甲基丙烯酸酯为交联剂,制备了咖啡因分子印迹聚合物(MIP)。与非印迹聚合物(NIP)相比,MIP对咖啡因具有更高的吸附容量和选择性,MIP和NIP对咖啡因的最大静态吸附量分别为28.1和16.5mg/g,相对选择因子为1.25。以咖啡因分子印迹聚合物为固相萃取填料,结合高效液相色谱(HPLC),建立了茶水中咖啡因浓度及人饮茶后血清中咖啡因浓度的检测方法。考察了洗脱剂种类和用量对咖啡因回收率的影响。当萃取柱依次以2mL水活化,水溶液上样,2mL水淋洗,6mL甲醇-乙酸(9∶1,V/V)洗脱,咖啡因在MIP固相萃取柱上的回收率达到97.5%,而在NIP柱上的回收率仅为54.9%。     

Preparation of molecularly imprinted polymers via atom transfer radical “bulk” polymerization

The first application of atom transfer radical “bulk” polymerization (ATRBP) in molecular imprinting is described, which provides molecularly imprinted polymers (MIPs) with obvious imprinting effects towards the template, very fast binding kinetics, and an appreciable selectivity over structurally related compounds. In comparison with the MIP prepared via the normally used traditional “bulk” free radical polymerization (BFRP), the MIPs obtained via ATRBP showed somewhat lower binding capacities and apparent maximum numbers N_max for high‐affinity sites as well as quite similar binding association constants K_a for high‐affinity sites and high‐affinity site densities, in contrast with the previous reports (e.g., nitroxide/iniferter‐mediated “bulk” polymerization provided MIPs with improved properties). This is tentatively ascribed to the occurrence of rather fast gelation process in ATRBP, which greatly restricted the mobility of the chemical species, leading to a heavily interrupted equilibrium between dormant species and active radicals and heterogeneous polymer networks. In addition, the general applicability of ATRBP was also confirmed by preparing MIPs for different templates. This work clearly demonstrates that applying controlled radical polymerizations (CRPs) in molecular imprinting not always benefits the binding properties of the resultant MIPs, which is of significant importance for the rational use of CRPs in generating MIPs with improved properties. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 532–541, 2010     

Synthesis and Evaluation of Molecularly Imprinted Polymers as Sorbents for Selective Extraction of Coumarins

Coumarin, 7-hydroxycoumarin and dicoumarol molecularly imprinted polymers (MIP) were synthesized by bulk polymerization. Methacrylic acid and 4-vinylpyridine were tested as functional monomers and methanol, ethanol, acetonitrile, toluene and chloroform were tested as porogens. The binding capabilities of the imprinted polymers were assessed by equilibrium binding analysis. Highest binding capacity was obtained for MIP prepared for the template 7-hydroxycoumarin synthesized in methacrylic acid as functional monomer, chloroform as porogen and methanol/water as analyte solvent. Scanning electron microscopy analysis documented its appropriate morphology. ATR-FTIR spectra confirmed successful polymerization of MIP. Coumarin structural analogues were employed to evaluate the polymer selectivity and it was found that polymer prepared for 7-hydroxycoumarin was selective for its template molecule. Kinetic studies showed relatively fast adsorption of analytes to MIPs (1 h). Rebinding properties of MIPs were evaluated by adsorption isotherms. The calculated data fitted well with experimental data showing that Freundlich isotherm is suitable for modelling the adsorption of tested coumarins on prepared MIPs. Applicability of polymer prepared for 7-hydroxycoumarin was tested for the selective extraction of coumarins from the sample of chicory.     

Extraction of lutetium(III) from aqueous solutions by employing a single fibre‐supported liquid membrane

Transport behaviour of Lu(III) across a polypropylene hollow fibre‐supported liquid membrane containing di(2‐ethylhexyl)phosphoric acid (DEHPA) in dihexyl ether as a carrier has been studied. The donor phase was LuCl₃ in the buffer solution consisting of 0.2 M sodium acetate at pH 2.5–5.0. A miniaturised system with a single hollow fibre has been operated in a batch mode. The concentration of Lu(III) was determined by indirect voltammetric method using Zn–EDTA complex. The effect of pH and volume of the donor phase, DEHPA concentration in the organic (liquid membrane) phase, the time of extraction and the content of the acceptor phase on the Lu(III) extraction and stripping behaviour was investigated. The results were discussed in terms of the pertraction and removal efficiency, the memory effect and the mean flux of Lu(III). The optimal conditions for the removal of ¹⁷⁷Lu(III) from labelled ¹⁷⁷Lu‐radiopharmaceuticals were discussed and identified. The removal efficiency of Lu(III) greater than 99% was achieved at pH of the donor phase between 3.5 and 5.0 using DEHPA concentration in the organic phase of 0.47 M and the ratio of the donor to the acceptor phase of 182.     

Synthesis and Molecular Recognition of Molecularly Imprinted Polymer with Ibuprofen as Template

Ibuprofen and ketoprofen are chemically similar non‐steroidal anti‐inflammatory drugs widely used in the treatment of arthritis. Using a molecular imprinting technique, a simple and rapid method was developed for the simultaneous separation and determination of ibuprofen and ketoprofen. Molecular imprinting introduces artificial binding sites into a synthetic polymer matrix, allowing it to exhibit selective rebinding of template molecules. Imprinted polymers can be regarded as an HPLC stationary phase, important for pharmaceutical analysis. Most molecularly imprinted polymers (MIPs) are synthesized by free radical polymerization of functional monomers, resulting in an excess of crosslinking monomers. In this study, MIPs have been prepared with a ibuprofen template, which can form intramolecular hydrogen bonds. Methacrylic acid (MAA) and ethyleneglycol dimethacrylate (EGDMA) were used as the functional monomer and cross‐linker, respectively. Bulk polymerization was carried out at 4 °C under UV radiation. The resulting MIP was ground into 25?44 μm particles, which were slurry‐packed into analytical columns. Template molecules were removed by methanol‐acetic acid (9:1, v/v). We evaluated the template binding performance of the MIP using HPLC, with ultraviolet (UV) detection at 234 nm. Chromatographic resolution of ibuprofen and ketoprofen on the MIPs were appraised using buffer/acetonitrile (45/55, v/v) as the mobile phase. Results show that the MIPs prepared using ibuprofen as the template had a significant molecular imprinting effect. The method was successfully applied to the separation and analysis of ibuprofen and ketoprofen in pharmaceuticals.     

Molecularly Imprinted Polymers with Mandelic Acid as Template

In this report, molecularly imprinted polymers (MIPs) with racemic and L-mandelic acid as the templates were synthesized. Several structural analogues were chosen to study the selectivity of the MIPs prepared using 4-vinylpyridine (4-VP) as the monomer (MIP_4-VP). At the same time, the chromatographic behaviors of the MIP using acrylamide (AA) as the monomer (MIP_AA) in two different mobile phases, acetonitrile and hexane/ethyl acetate (1:1, v/v), were investigated and the separation of the enantiomers was tried. The results indicated that MIP_4-VP had great retention with a template comparable to other analogues. However, no difference in the k′ values of the enantiomers was observed, as the interaction between the polymer and the enantiomers was mainly dependent on the acidity, which showed no difference. The MIP_AA showed a more obvious imprinting effect for the template in hexane/ethyl acetate (1:1, v/v) than in acetonitrile. But the separation of the enantiomers was not achieved even in the less polar solvent, though there was an obvious difference between the retention time of L-MA and D-MA on the L-MA imprinted polymer.     

Continuous flow liquid membrane extraction: a novel automatic trace-enrichment technique based on continuous flow liquid-liquid extraction combined with supported liquid membrane

Combining the continuous flow liquid-liquid extraction (CFLLE) and supported liquid membrane (SLM) extraction, a novel aqueous-aqueous extraction technique that we termed continuous flow liquid membrane extraction (CFLME) is developed for trace-enrichment. The analyte was firstly extracted into the organic phase in the CFLLE step, then transported onto the organic liquid membrane that formed on the surface of the micro porous membrane of the SLM equipment. Finally, it passed through the liquid membrane and was trapped by the acceptor. Aspects related to CFLME were studied by using dichloromethane as liquid membrane, and sulfonylurea herbicides as model compounds. An enrichment factor of over 1000 was obtained when 10 μg l⁻¹ of MSM was enriched for 120 min by this technique. The drawbacks of only a few organic solvents can be selected as liquid membrane with a limited lifetime in SLM operation was overcome. In this CFLME method, almost all solvents that used in the conventional liquid-liquid extraction (LLE) can be adopted and the lifetime of liquid membrane is no longer a problem.