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Highlights: [•] A high-throughput electromembrane extraction platform has been developed. [•] In total 96 samples were processed in parallel within 10min of extraction. [•] The final extraction was directly compatible with mass spectrometry. [ABSTRACT FROM AUTHOR]

This paper describes the concept of parallel electromembrane extraction (Pa-EME) with flat membranes in a multiwell format for the first time. The setup is based on a multiwell plate and provided simultaneous and selective isolation, cleanup, and enrichment of several human plasma samples as well as LC-MS-compatible extracts within 8 min of extraction. Undiluted human plasma samples spiked with four antidepressant drugs were added to separate wells in the donor plate. Subsequently, the samples were extracted with Pa-EME. The four drugs migrated electrokinetically from undiluted human plasma through a flat polypropylene membrane impregnated with 2-nitrophenyl octyl ether, and were isolated into formic acid. Extraction time, extraction voltage, agitation rate, sample volume, and acceptor solution volume were all optimized with an experimental design. The optimal conditions were as follows: The agitation rate was 1,040 rpm, and an extraction voltage of 200 V was applied. The sample volume and acceptor solution volume was 240 and 70 μL, respectively. The extraction was continued for 8 min. Eventually, the extracts were analyzed by LC-MS/MS. The combination of Pa-EME with LC-MS/MS provided quantitation limits below the therapeutic level and reported relative standard deviations in the range 5-13 %. Linear calibration curves were obtained for all analytes, and the correlation coefficients were above 0.9974 in the range 1-400 ng mL. The drug concentrations from two subjects treated with quetiapine and sertraline were successfully determined with Pa-EME combined with LC-MS/MS. Post-column infusion experiments demonstrated that Pa-EME provided extracts free from interfering matrix components. [ABSTRACT FROM AUTHOR]

The present work describes the first systematic study of electromembrane extraction (EME) from biological matrices under physiological conditions. Six basic drugs with protein binding in the range of 20–97% were extracted from untreated human plasma and whole blood through a supported liquid membrane (SLM) consisting of 1-ethyl-2-nitrobenzene impregnated in the walls of a hollow fiber, and into an acidified aqueous solution inside the lumen of the fiber. The electrical potential difference over the membrane reduced the protein binding of the drugs and transported the free drug fraction over the membrane. Recoveries in the range 25–65% were obtained with 10-min extraction time and an applied voltage of only 10 V over the SLM. Interday precision better than 20% RSD and linearity in the range 0.5–10 µg/mL were obtained for nortriptyline and methadone. Extraction from untreated whole blood was also demonstrated with recoveries in the range 19–51%. [ABSTRACT FROM AUTHOR]

Abstract: In this review, we discuss three different approaches to liquid-liquid extraction (LLE) driven by an electrical field (dc): [(1)] electro extraction, by which ionic analytes are extracted from a stagnant organic solution (immiscible with water) into water; [(2)] electrochemically-modulated LLE (known as ITIES extraction, where ITIES means “interface between two immiscible electrolyte solutions”), by which ionic analytes are extracted from a flowing aqueous sample and into a stationary organo-gel; and, [(3)] electro-membrane extraction, by which ionic analytes are extracted from an agitated aqueous sample, through an organic solvent (supported liquid membrane) sustained in the pores in the wall of a porous hollow fiber, and into an aqueous acceptor inside the lumen of the hollow fiber. We review the literature with respect to these techniques, which we compare in terms of performance and working principles, and outline the promising aspects of using electrical fields to enhance and to manipulate LLE. In conclusion, we identify LLE driven by electrical fields as an important field for future development in sample preparation for chromatography and electrophoresis. [Copyright &y& Elsevier]

Describes the liquid-liquid-liquid microextraction (LLLME) for sample preparation of biological fluids prior to capillary electrophoresis. Use of methamphetamine as model compound; Analysis of the acceptor solutions by capillary zone electrophoresis; Use of LLLME as a technique for sample cleanup.

Abstract: In this paper, extraction kinetics was investigated experimentally and theoretically in hollow fiber liquid-phase microextraction (HF-LPME) and electromembrane extraction (EME) with the basic drugs droperidol, haloperidol, nortriptyline, clomipramine, and clemastine as model analytes. In HF-LPME, the analytes were extracted by passive diffusion from an alkaline sample, through a (organic) supported liquid membrane (SLM) and into an acidic acceptor solution. In EME, the analytes were extracted by electrokinetic migration from an acidic sample, through the SLM, and into an acidic acceptor solution by application of an electrical potential across the SLM. In both HF-LPME and EME, the sample (donor solution) was found to be rapidly depleted for analyte. In HF-LPME, the mass transfer across the SLM was slow, and this was found to be the rate limiting step of HF-LPME. This finding is in contrast to earlier discussions in the literature suggesting that mass transfer across the boundary layer at the donor–SLM interface is the rate limiting step of HF-LPME. In EME, mass transfer across the SLM was much more rapid due to electrokinetic migration. Nevertheless, mass transfer across the SLM was rate limiting even in EME. Theoretical models were developed to describe the kinetics in HF-LPME, in agreement with the experimental findings. In HF-LPME, the extraction efficiency was found to be maintained even if pH in the donor solution was lowered from 10 to 7–8, which was below the pKa-value for several of the analytes. Similarly, in EME, the extraction efficiency was found to be maintained even if pH in the donor solution increased from 4 to 11, which was above the pKa-value for several of the analytes. The two latter experiments suggested that both techniques may be used to effectively extract analytes from samples in a broader pH range as compared to the pH range recommended in the literature. [Copyright &y& Elsevier]

Abstract: Citalopram, loperamide, methadone, paroxetine, pethidine, and sertraline were extracted exhaustively with electromembrane extraction (EME) by increasing the number of hollow fibers from one to three. Experiments reported recoveries in the range 97–115% from 1000μl spiked water samples. EME was accomplished with 200V as extraction voltage, the extraction time was set to 10min (equilibrium), and the extraction unit was subjected to 1200 revolutions per minute (rpm). The same experiment with different geometry in a stagnant system conducted with 21μl acceptor solution provided recoveries from 50μl undiluted human plasma (pH 7.4) in the range of 56–102% for the six basic model substances. In each experiment the acceptor solution was distributed into three separately hollow fibers in the same sample vial. The importance of an electrical field was verified by comparing EME with liquid-phase microextraction (LPME) under optimal conditions and demonstrated that the time needed to reach equilibrium was reduced by EME. EME–LC/MS provided linearity >0.99 (r 2 values) for the six basic model substances, and the repeatability within the low therapeutic range (10ng/ml) was in the range 5.1–21.4% RSD. LC–MS provided estimated limit of quantification (S/N =10) in the range 0.6–3.2ng/ml. Eventually, patient samples from a reference laboratory were analyzed and provided reliable results with a relative difference <14% compared to stated values from the reference laboratory. [Copyright &y& Elsevier]

Liquid-phase microextraction (LPME) based on disposable porous polypropylene hollow fibers was evaluated for the extraction of hydrophobic basic drugs from human breast milk. Direct LPME from breast milk samples provided low recoveries (18–38%) because the drugs were partially bound to the sample matrix (fat). Therefore, prior to extraction, the breast milk was acidified and the majority of fat was removed by centrifugation. The pH-reduction in the breast milk was performed to release drugs interacting with the matrix. From the supernatant, where pH was adjusted into the alkaline region with NaOH to deionize the analytes, the drugs were extracted through a thin layer of polyphenyl-methylsiloxane present in the pores of a porous hollow fiber and into 15 μl of 10 mM HCl as acceptor solution present inside the lumen of the hollow fiber. Subsequently, the acceptor solution was directly subjected to capillary electrophoresis (CE). For four antidepressant drugs, recoveries in the range 42–69% were obtained from breast milk, the drugs were enriched by a factor of 14–23 during LPME, excellent sample clean-up was observed, linearity (r>0.99) was obtained in the range 50–500 ng/ml, and the extractions were found to be independent of the fat content in the breast milk samples. [Copyright &y& Elsevier]

Mathematical descriptions for extraction recovery and enrichment were applied for liquid-phase microextraction (LPME) and comparison with conventional two- and three-phase liquid–liquid extraction techniques (LLE) was made. The LPME theoretical calculations were verified by experimental determination of actual partition coefficients and by data obtained with LPME in a robust hollow fibre formate. With hollow fibre LPME operated in the two-phase mode, analytes were extracted from 1 to 4 ml aqueous samples into 25–50 μl of an organic solvent present in the pores and in the lumen of the porous hollow fibres. Compared with conventional two-phase LLE, two-phase LPME provided substantially higher enrichments for compounds with relatively large partition coefficients (Korg/d>500). In contrast, because of the large volume of organic solvent relative to the sample volume, LLE provided high recovery and moderate enrichment even for compounds with relatively low partition coefficients (Korg/d>5). Thus, two-phase LPME may be used for substantially enhanced extraction selectivity and enrichment of relatively hydrophobic analytes as compared with LLE whereas conventional two-phase LLE is superior for more hydrophilic analytes. Similar results were found for three-phase LPME where analytes where extracted from 1 to 4 ml aqueous samples through approximately 20 μl organic solvent immobilized within the pores of the hollow fibre and into 25 μl of an aqueous acceptor solution inside the lumen of the hollow fibre. The fundamental differences of LPME and LLE were further demonstrated with practical experiments on extraction of the basic drugs promethazine, methadone, and haloperidol from human plasma and urine. [Copyright &y& Elsevier]

Abstract: Electromembrane extraction (EME) at low voltage (0–15V) of 29 different basic model drug substances was investigated. The drug substances with log P <2.3 were not extracted at voltages less than 15V. Extraction of drug substances with log P ≥2.3 and with two basic groups were also effectively suppressed by the SLM at voltages less than 15V. Drug substances with log P ≥2.3 and with one basic group were all extracted at low voltages and with a strong compound selectivity which appeared to have some influence from the polar surface area of the compound. For this group of substances, recoveries varied between 0 and 23% at 5V, whereas, recoveries varied between 5.5 and 51% at 15V. Based on mass transfer differences related to charge, polarity, and polar surface, highly selective extractions of drug substances were demonstrated from human plasma, urine, and breast milk. An initial evaluation at low voltage (5V) was compared with similar extractions at a more normal voltage level (50V), and this supported that reliable data can be obtained under these low-voltage (mild) conditions by EME. [Copyright &y& Elsevier]

Abstract: Liquid-phase microextraction (LPME) based on polypropylene hollow fibers was evaluated for the extraction of the post-harvest fungicides thiabendazole (TBZ), carbendazim (CBZ) and imazalil (IMZ) from orange juices. Direct LPME was performed without any sample pretreatment prior to the extraction, using a simple home-built equipment. A volume of 500μL of 840mM NaOH was added to 3mL of orange juice in order to compensate the acidity of the samples and to adjust pH into the alkaline region. Analytes were extracted in their neutral state through a supported liquid membrane (SLM) of 2-octanone into 20μL of a stagnant aqueous solution of 10mM HCl inside the lumen of the hollow fiber. Subsequently, the acceptor solution was directly subjected to analysis. Capillary electrophoresis (CE) was used during the optimization of the extraction procedure. Working under the optimized extraction conditions, LPME effectively extracted the analytes from different orange juices, regardless of different pH or solid material (pulp) present in the sample, with recoveries that ranged between 17.0 and 33.7%. The analytical performance of the method was evaluated by liquid chromatography coupled with mass spectrometry (LC/MS). This technique provided better sensitivity than CE and permitted the detection below the μgL−1 level. The relative standard deviations of the recoveries (RSDs) ranged between 3.4 and 10.6%, which are acceptable values for a manual microextraction technique without any previous sample treatment, using a home-built equipment and working under non-equilibrium conditions (30min extraction). Linearity was obtained in the range 0.1–10.0μgL−1, with r =0.999 and 0.998 for TBZ and IMZ, respectively. Limits of detection were below 0.1μgL−1 and are consistent with the maximum residue levels permitted for pesticides in drinking water, which is the most restrictive regulation applicable for these kinds of samples. It has been demonstrated the suitability of three-phase LPME for the extraction of pesticides from citrus juices, suppressing any pretreatment step such as filtration or removal of the solid material from the sample, that may potentially involve a loss of analyte. [Copyright &y& Elsevier]

Abstract: In the current work, droplet-membrane-droplet liquid-phase microextraction (LPME) under totally stagnant conditions was presented for the first time. Subsequently, implementation of this concept on a microchip was demonstrated as a miniaturized, on-line sample preparation method. The performance level of the lab-on-a-chip system with integrated microextraction, capillary electrophoresis (CE) and laser-induced fluorescence (LIF) detection in a single miniaturized device was preliminarily investigated and characterized. Extractions under stagnant conditions were performed from 3.5 to 15μL sample droplets, through a supported liquid membrane (SLM) sustained in the pores of a small piece of a flat polypropylene membrane, and into 3.5–15μL of acceptor droplet. The basic model analytes pethidine, nortriptyline, methadone, haloperidol, and loperamide were extracted from alkaline sample droplets (pH 12), through 1-octanol as SLM, and into acidified acceptor droplets (pH 2) with recoveries ranging between 13 and 66% after 5min of operation. For the acidic model analytes Bodipy FL C5 and Oregon Green 488, the pH conditions were reversed, utilizing an acidic sample droplet and an alkaline acceptor droplet, and 1-octanol as SLM. As a result, recoveries for Bodipy FL C5 and Oregon Green 488 from human urine were 15 and 25%, respectively. [Copyright &y& Elsevier]

Abstract: Electromembrane extraction (EME) of basic drugs from 10μL sample volumes was performed through an organic solvent (2-nitrophenyl octyl ether) immobilized as a supported liquid membrane (SLM) in the pores of a flat polypropylene membrane (25μm thickness), and into 10μL 10mM HCl as the acceptor solution. The driving force for the extractions was 3–20V d.c. potential sustained over the SLM. The influence of the membrane thickness, extraction time, and voltage was investigated, and a theory for the extraction kinetics is proposed. Pethidine, nortriptyline, methadone, haloperidol, and loperamide were extracted from pure water samples with recoveries ranging between 33% and 47% after only 5min of operation under totally stagnant conditions. The extraction system was compatible with human urine and plasma samples and provided very efficient sample pretreatment, as acidic, neutral, and polar substances with no distribution into the organic SLM were not extracted across the membrane. Evaluation was performed for human urine, providing linearity in the range 1–20μg/mL, and repeatability (RSD) in average within 12%. [Copyright &y& Elsevier]

Abstract: Recently, we demonstrated for the first time liquid-phase microextraction (LPME) of polar drugs based on carrier mediated transport. In this new extraction technique, selected analytes were extracted as ion-pairs from small volumes of biological samples, through a thin layer of a water immiscible organic solvent immobilised in the pores of a porous hollow fibre (liquid membrane), and into a μl volume of an acidic aqueous acceptor solution placed inside the lumen of the hollow fibre. In the current paper, this new extraction technique was combined with liquid chromatography–mass spectrometry (LC–MS) for the first time. Carrier mediated LPME was evaluated for several new model drugs (0.01&#60;log P &#60;1.76), the sample clean-up aspects were investigated in detail, and this new extraction technique was fully validated for the first time. Extractions were performed from 50μl of human plasma samples, which provided sufficient material in combination with LC–MS. Sodium octanoate (50mM) was added to the sample as carrier, 1-octanol (≈15μl) was used as the liquid membrane in the wall of the hollow fibre, and 50mM HCl was utilized as acceptor solution in the lumen of the hollow fibre. The addition of carrier to the samples was found to significantly improve extraction recoveries for the polar drugs tested, providing recoveries in the range 16–78%. Validation was accomplished for atenolol and cimetidine. Limits of quantification (S/N=5) from 50μl of plasma were 25 and 50ng/ml for atenolol and cimetidine, respectively. The intra-day precision (R.S.D.) ranged from 7.8 to 17.2% and from 9.5 to 14.1% for atenolol and cimetidine, respectively, and corresponding inter-day precisions (R.S.D.) were within 6.7–1.4% and 7.7–20.3%. The method was linear in the range 25–1500ng/ml for atenolol (r =0.992), and 50–3500ng/ml for cimetidine (r =0.976). The accuracy of the method was found to be in range 89.1–99.6% and 83.4–86% for atenolol and cimetidine, respectively. The sample clean-up obtained by carrier mediated LPME was excellent, providing a significantly lower back-ground level in total ion current chromatograms by LC–MS as compared to protein precipitation. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

A disposable device for liquid-phase microextraction (LPME) based on porous polypropylene hollow fibres has recently been introduced. In the present paper, LPME was combined with capillary electrophoresis (CE) and the combination was for the first time evaluated for chiral determination of drugs in biological matrices. The chiral antidepressant drug mianserin was selected as model compound. The mianserin enantiomers were extracted from 0.5 ml of plasma added internal standard and made alkaline with 0.25 ml of 2 M NaOH. The unionised analytes were extracted into di-n-hexyl ether impregnated in the pores of the hollow fibre, and into an acidic solution inside the hollow fibre. This resulted in a three-phase system where the extracts were aqueous, and hence directly compatible with the CE system. Efficient sample clean-up was seen and the extraction recovery was 80% for both enantiomers. Discrimination between the enantiomers in the extraction system was not observed. The limit of quantitation (S/N=10; 12.5 ng/ml for both enantiomers) and the limit of detection (S/N=3; 4 ng/ml for both enantiomers) were below the therapeutic range for mianserin. The method was validated and successfully applied to determine R- and S-mianserin in plasma samples from seven patients treated with mianserin, indicating that LPME–CE is a promising combination for analysis of racemic drugs present in low concentrations in biological matrices. [Copyright &y& Elsevier]