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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]

Abstract: 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. [Copyright &y& Elsevier]

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]

Abstract: 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 1–10V applied over the SLM. Extractions from 1ml standard solutions prepared in 10mM HCl for 5min and with a potential of 10V demonstrated analyte recoveries of 50–93% in 25μl of 10mM HCl as acceptor solution. This corresponds to enrichment factors of 20–37. Similar results were obtained with a common 9V 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 5min of extraction. Excellent selectivity was demonstrated as no interfering peaks were detected. Standard curves in the range of 0.0625–0.625μg/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. [Copyright &y& Elsevier]

Abstract: 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 25μl 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 25μl 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 (150μl), 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. [Copyright &y& Elsevier]

Abstract: Electrokinetic cross membrane extraction of acidic drugs was demonstrated for the first time. The acidic drugs were extracted from an alkaline aqueous donor solution (300μl), 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 (30μl) 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 50V as the driving force, and with pH 12.0 in both the donor and acceptor solutions, respectively (NaOH). Equilibrium extraction conditions were obtained after 5min of operation with the whole assembly agitated at 1200rpm. 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. [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: The simultaneous extraction of acidic and basic analytes from a particular sample is a challenging task. In this work, electromembrane extraction (EME) of acidic non-steroidal anti-inflammatory drugs and basic β-blockers in a single step was carried out for the first time. It was shown that by designing an appropriate compartmentalized membrane envelope, the two classes of drugs could be electrokinetically extracted by a 300V direct current electrical potential. This method required only a very short 10-min extraction time from a pH-neutral sample, with a small amount (50μL) of organic solvent (1-octanol) as the acceptor phase. Analysis was carried out using gas chromatography–mass spectrometry after derivatization of the analytes. Extraction parameters such as extraction time, applied voltage, pH range, and concentration of salt added were optimized. The proposed EME technique provided good linearity with correlation coefficients from 0.982 to 0.997 over a concentration range of 1–200μgL−1. Detection limits of the drugs ranged between 0.0081 and 0.26μgL−1, while reproducibility ranged from 6 to 13% (n =6). Finally, the application of the new method to wastewater samples was demonstrated. [ABSTRACT FROM AUTHOR]

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]