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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(-1). 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.

Background: This paper reports development of a new approach towards analytical liquid-liquid-liquid membrane extraction termed parallel artificial liquid membrane extraction. A donor plate and acceptor plate create a sandwich, in which each sample (human plasma) and acceptor solution is separated by an artificial liquid membrane. Parallel artificial liquid membrane extraction is a modification of hollow-fiber liquid-phase microextraction, where the hollow fibers are replaced by flat membranes in a 96-well plate format., Results: Four basic drugs (pethidine, nortriptyline, methadone and haloperidol) were extracted from human plasma in 30 min, followed by analysis with LC-MS/MS. Extraction recoveries for the model analytes were in the range of 34-74% from human plasma. LOQs were in the range of 0.01-0.35 ng/ml, linearity above 0.9955 for all drugs and with RSD values below 12%., Conclusion: Liquid-liquid-liquid membrane extraction was successfully performed in a slightly modified commercially available 96-well plate format.

Samples of 10 μL of whole blood containing citalopram, loperamide, methadone, and sertraline as model substances were spotted on alginate and chitosan foams as sampling media. After drying and storage at room temperature, the punched out dried blood spot and the foam was dissolved in 300 μL of 1 mM HCl. With alginate foam as sampling medium, the analytes dissolved completely after 3 min. Enrichment and cleanup was performed with electromembrane extraction for 10 min. The analytes were collected in 21 μL of 10 mM formic acid as the acceptor phase, and the extracts were analyzed by liquid chromatography-mass spectrometry (LC-MS). Sample preparation of blood spots on commercial cards was also performed (Whatman FTA DMPK and Agilent Bond Elut DMS) using elution procedures recommended by the manufacturers. The recoveries obtained with the commercial cards were lower for most of the model analytes compared to the recoveries obtained with alginate and chitosan foams as sampling media. The procedure used for Agilent Bond Elut DMS showed higher recoveries than the procedure used for Whatman FTA DMPK-A, but the time needed for sample preparation was significantly longer (nearly 2 h). The stability of the model substances on the alginate foam was acceptable within 50 days of storage. The limit of quantification (LOQ) defined as S/N = 10, was 1.2, 5.5, 2.0, and 5.3 ng/mL for citalopram, loperamide, methadone, and sertraline, respectively. Linear calibration graphs were obtained in the range 17.5-560 ng/mL with r(2) values 0.983-0.995, and the relative standard deviations were below 20%.

Electromembrane extraction (EME) at low voltage (0-15 V) of 29 different basic model drug substances was investigated. The drug substances with logP<2.3 were not extracted at voltages less than 15 V. Extraction of drug substances with logP≥2.3 and with two basic groups were also effectively suppressed by the SLM at voltages less than 15 V. Drug substances with logP≥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 5 V, whereas, recoveries varied between 5.5 and 51% at 15 V. 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 (5 V) was compared with similar extractions at a more normal voltage level (50 V), and this supported that reliable data can be obtained under these low-voltage (mild) conditions by EME., (Copyright © 2012 Elsevier B.V. All rights reserved.)

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 © 2011 Elsevier B.V. All rights reserved.)

For the first time, haloacetic acids and aromatic acetic acids were extracted from wastewater samples using electromembrane extraction (EME). A thin layer of toluene immobilized on the walls of a polypropylene membrane envelope served as an artificial supported liquid membrane (SLM). The haloacetic acids (HAAs) (chloroacetic acid, dichloroacetic acid, and trifluoroacetic acid) and aromatic acetic acids (phenylacetic acid and p-hydroxyphenylacetic acid) were extracted through the SLM and into an alkalized aqueous buffer solution. The buffer solution was located inside the membrane envelope. The electrical potential difference sustained over the membrane acted as the driving force for the transport of haloacetic acids into the membrane by electrokinetic migration. After extraction, the extracts were analyzed by high-performance liquid chromatography-ultraviolet detection. The detection limits were between 0.072 and 40.3 ng L(-1). The calibration plot linearity was in the range of 5 and 200 μg L(-1) while the correlation coefficients for the analytes ranged from 0.9932 to 0.9967. Relative recoveries were in the range of 87-106%. The extraction efficiency was found to be comparable to that of solid-phase extraction., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Electromembrane extraction (EME) of basic drugs from 10 microL 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 (25 microm thickness), and into 10 microL 10 mM HCl as the acceptor solution. The driving force for the extractions was 3-20 V 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 5 min 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 1-20 microg/mL, and repeatability (RSD) in average within 12%.

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 microg/mL were obtained for nortriptyline and methadone. Extraction from untreated whole blood was also demonstrated with recoveries in the range 19-51%.

In hollow fiber membrane liquid-phase microextraction (LPME), target analytes are extracted from aqueous samples and into a supported liquid membrane (SLM) sustained in the pores in the wall of a small porous hollow fiber, and further into an acceptor phase present inside the lumen of the hollow fiber. The acceptor phase can be organic, providing a two-phase extraction system compatible with capillary gas chromatography, or the acceptor phase can be aqueous resulting in a three-phase system compatible with high-performance liquid chromatography or capillary electrophoresis. Due to high enrichment, efficient sample clean-up, and the low consumption of organic solvent, substantial interest has been devoted to LPME in recent years. This paper reviews important applications of LPME with special focus on bioanalytical and environmental chemistry, and also covers a new possible direction for LPME namely electromembrane extraction, where analytes are extracted through the SLM and into the acceptor phase by the application of electrical potentials.

Thirty-five different basic drugs were extracted by electro membrane extraction (EME), from acidified samples containing HCl as the BGE, through an organic solvent immobilized in the pores in the wall of a porous hollow fiber (supported liquid membrane, SLM), and into an acidified acceptor solution (HCl) in the lumen of the hollow fiber by the application of an electrical potential difference of 50 V. With 2-nitrophenyl pentyl ether (NPPE) as the SLM, and with 10 mM HCl as BGE in the sample and acceptor solution, singly charged basic drugs with log P >2 were extracted with recoveries in the range 30-81% within 5 min. For doubly charged basic drugs, extraction was effectively enhanced by decreasing the concentration of HCl in the sample from 10 to 0.1 mM, reducing the ionization of the analytes. For medium polar analytes (1 < log P < 2), an ion balance of 0.01 was combined with addition of tris-(2-ethylhexyl) phosphate (TEHP) to the SLM, and this provided recoveries in the range 36-70%. The ion balance was defined as the concentration ratio of BGE between the sample and the acceptor solution. For the most polar drugs (log P <1), EME was accomplished with an ion balance of 0.01 and with di-(2-ethylhexyl) phosphate (DEHP) added to the SLM, but in spite of this, recoveries were in the range of only 4-17%.

The present work has for the first time demonstrated electromembrane extraction (EME) at voltages obtainable by common batteries. Five basic drugs were extracted from acidified aqueous sample solutions, across a supported liquid membrane (SLM) consisting of 1-isopropyl-4-nitrobenzene impregnated in the walls of a hollow fiber, and into an acidified aqueous acceptor solution present inside the lumen of the hollow fiber with potential differences of 1-10 V applied over the SLM. Extractions from 1 ml standard solutions prepared in 10mM HCl for 5 min and with a potential of 10 V demonstrated analyte recoveries of 50-93% in 25 microl of 10mM HCl as acceptor solution. This corresponds to enrichment factors of 20-37. Similar results were obtained with a common 9 V battery as power supply. Recoveries from low-voltage EME on human plasma, urine, and breast milk diluted with acetate buffer (pH 4) demonstrated recoveries in the range of 37-55% after 5 min of extraction. Excellent selectivity was demonstrated as no interfering peaks were detected. Standard curves in the range of 0.0625-0.62 5 microg/ml demonstrated correlation coefficients of 0.994-0.999. Extraction recoveries from human plasma, urine or breast milk were not found to be sensitive towards individual variations. The results show that low-voltage EME has a future potential as a simple, selective, and time-efficient sample preparation technique of biological fluids.

The present work has for the first time described and verified a theoretical model of the analytical extraction process electro-membrane extraction (EME), where target analytes are extracted from an aqueous sample, through a thin layer of 2-nitrophenyl octylether immobilized as a supported liquid membrane (SLM) in the pores in the wall of a porous hollow fibre, and into an acceptor solution present inside the lumen of the hollow fibre by the application of an electrical potential difference. The mathematical model was based on the Nernst-Planck equation, and described the flux over the SLM. The model demonstrated that the magnitude of the electrical potential difference, the ion balance of the system, and the absolute temperature influenced the flux of analyte across the SLM. These conclusions were verified by experimental data with five basic drugs. The flux was strongly dependent of the potential difference over the SLM, and increased potential difference resulted in an increase in the flux. The ion balance, defined as the sum of ions in the donor solution divided by the sum of ions in the acceptor solution, was shown to influence the flux, and high ionic concentration in the acceptor solution relative to the sample solution was advantageous for high flux. Different temperatures also led to changes in the flux in the EME system.

The present work has for the first time compared extraction of basic analytes across a supported liquid membrane (SLM) based on (1) passive diffusion in a pH gradient sustained over the SLM and (2) electrokinetic migration in an electrical field sustained over the SLM. For the passive diffusion experiments, performed as liquid-phase microextraction (LPME), five basic drugs were extracted under strong agitation from alkaline samples (10mM NaOH), through 2-nitrophenyl octylether immobilized in the pores of a porous hollow fibre of polypropylene (SLM), and into 25 microl of 10mM HCl as the acceptor solution. The experiments based on electrokinetic migration, performed as electro membrane isolation (EMI), were conducted under strong agitation from acidic samples (10mM HCl), through the same SLM as in LPME, and into 25 microl of 10mM HCl as the acceptor solution. Whereas LPME relied on diffusion and to some extent also convection as the principal mechanisms of mass transfer, mass transfer in EMI also included a strong contribution from electrokinetic migration. Thus, extraction kinetics was improved by a factor between 6 and 17 utilizing EMI instead of LPME. This major difference in terms of speed was especially pronounced from small sample volumes (150 microl), and suggest that EMI may be a very interesting future concept for miniaturized sample preparation. In addition to improved extraction kinetics, extraction rates were strongly compound dependent in EMI, opening the possibility to control the extraction selectivity by the extraction time.

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

In this work, three-phase liquid-phase microextraction (LPME) based on a supported liquid membrane (SLM) sustained in the wall of a hollow fiber was investigated with special focus on optimization of the experimental procedures in terms of recovery and repeatability. Recovery data for doxepin, amitriptyline, clomipramine, and mianserin were in the range of 67.8-79.8%. Within-day repeatability data for the four basic drugs were in the range of 4.1-7.7%. No single factor was found to be responsible for these variations, and the variability was caused by several factors related to the LPME extractions as well as to the final HPLC determination. Although the volume of the SLM varied within 0.4-3.1% RSD depending on the preparation procedure, and the volume of the acceptor solution varied within 4.8% RSD, both recoveries and repeatability were found to be relative insensitive to these variations. Thus, the handling of microliters of liquid in LPME was not a very critical factor, and the preparation of the SLM was accomplished in several different ways with comparable performance. Reuse of hollow fibers was found to suffer from matrix effects due to built-up of analytes in the SLM, whereas washing of the hollow fibers in acetone was beneficial in terms of recovery, especially for the extraction of the most hydrophobic substances. Several of the organic solvents used in the literature as SLM suffered from poor long-term stability, but silicone oil AR 20 (polyphenylmethylsiloxane), 2-nitrophenyl octyl ether (NPOE), and dodecyl acetate (DDA) all extracted with unaltered performance even after 60 days of storage at room temperature.

Twenty different basic drugs were electrokinetically extracted across a thin artificial organic liquid membrane with a 300 V d.c. electrical potential difference as the driving force. From a 300 microl aqueous sample (acidified corresponding to 10mM HCl), the drugs were extracted for 5 min through a 200 microm artificial liquid membrane of a water immiscible organic solvent immobilized in the pores of a polypropylene hollow fiber, and into a 30 microl aqueous acceptor solution of 10mM HCl inside the lumen of the hollow fiber. Hydrophobic basic drugs (logP>1.7) were effectively isolated utilizing 2-nitrophenyl octyl ether (NPOE) as the artificial liquid membrane, with recoveries up to 83%. For more hydrophilic basic drugs (logP<1.0), a mixture of NPOE and 25% (w/w) di-(2-ethylhexyl) phosphate (DEHP) was required to ensure efficient extraction, resulting in recoveries up to 75%. DEHP was expected to act as an ion-pair reagent ion-pairing the protonated hydrophilic drugs at the interface between the sample and the membrane, resulting in permeation of the interface.

Basic drug substances were transported across a thin artificial organic liquid membrane by the application of 300 V d.c. From a 300 microl aqueous donor compartment (containing 10 mM HCl), the drugs migrated through a 200 microm artificial liquid membrane of 2-nitrophenyl octyl ether immobilized in the pores of a polypropylene hollow fiber, and into a 30 microl aqueous acceptor solution of 10 mM HCl inside the lumen of the hollow fiber. The transport was forced by an electrical potential difference sustained over the liquid membrane, resulting in electrokinetic migration of drug substances from the donor compartment to the acceptor solution. Within 5 min of operation at 300 V, pethidine, nortriptyline, methadone, haloperidol, and loperamide were extracted with recoveries in the range 70-79%, which corresponded to enrichments in the range 7.0-7.9. The chemical composition of the organic liquid membrane strongly affected the permeability, and may serve as an efficient tool for controlling the transport selectivity. Water samples, human plasma, and human urine were successfully processed, and in light of the present report, electrokinetic migration across thin artificial liquid membranes may be an interesting tool for future isolation within chemical analysis.