Micro-electromembrane extraction (μ-EME) was presented for the selective extraction of four main β-lactam antibiotics (penicillin, phenoxypenicillin, ampicillin, and amoxicillin) from complex samples. A volatile solvent (ethyl acetate or chloroform) was sandwiched between a plug of the complex sample and another plug of an aqueous acceptor solution in a transparent polymeric tube and formed the so-called free liquid membrane (FLM). The use of the FLM eliminated the evaporation of the solvent and enabled the μ-EME of the antibiotics, which was carried out by the application of DC voltage to the terminal aqueous solutions. The drugs in the complex sample were selectively transferred through the FLM to the acceptor solution, which was directly used for their determination by micellar electrokinetic chromatography with ultraviolet detection (MEKC-UV). The μ-EME was characterized by sub-μA electric currents, high elimination of matrix components, high stability of operational solutions, and suitability for extracting undiluted complex samples. The μ-EME/MEKC-UV method yielded good analytical repeatability (RSDs of peak areas ≤5%), extraction recoveries (40-84%), accuracy (92-105%) and linearity over one and a half order of magnitude (R2 ≥ 0.9998), and was applied to the determination of the four β-lactam antibiotics in human serum and waste water at clinically and environmentally relevant concentration levels. Further improvement in the method sensitivity was achieved by changing the μ-EME tube geometry (conical shape) and increasing the complex sample volume (100 μL). The analytes were enriched by factors of 7.6-11.5, the limits of detection dropped down to less than 18 ng/mL, and the modified μ-EME/MEKC-UV method enabled the trace determination of β-lactam antibiotics in complex samples.
- MeSH
- Anti-Bacterial Agents MeSH
- beta-Lactams MeSH
- Electricity * MeSH
- Humans MeSH
- Membranes, Artificial * MeSH
- Solvents MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
A two-phase micro-electromembrane extraction (μ-EME) using a floating drop of an organic solvent was presented for rapid and efficient pretreatment of complex biological samples. The μ-EME system consisted of a glass vial containing aqueous sample (donor solution) and a small drop of a water-immiscible organic solvent (4-nitrocumene), which was floating on the surface of the aqueous solution in form of a free liquid membrane (FLM). The vial geometry and the optimized volume ratios of the donor and the FLM ensured a stable position of the FLM in the center of the vial during μ-EME, and one electrode of a d.c. power supply was inserted directly into the FLM while the other electrode was placed into the aqueous sample. The active surface area of the floating drop FLM contacting the sample was considerably larger in comparison to formerly reported μ-EME formats employing FLMs and resulted in a faster and a more efficient transfer of target analytes from the sample to the FLM. Four basic drugs (nortriptyline, papaverine, loperamide, and haloperidol) were selected as model analytes and were extracted from physiological solution, human urine, and dried blood spot samples. At the optimized μ-EME conditions (250 V, 15 min, 300 rpm, acidic donor) and the optimized ratio of the sample to the FLM volume (500:14 μL), extraction recoveries between 49 and 100% and enrichment factors up to 35.7 were achieved. Quantitative analyses of the basic drugs in the resulting FLMs (diluted with methanol) were performed by capillary electrophoresis with ultraviolet detection and demonstrated excellent repeatability (RSD ≤ 4.9%) and linearity (r2 ≥ 0.9997), and low limits of detection (5-28 ng/mL) of the method.
- Publication type
- Journal Article MeSH
A simple sample injection procedure compatible with commercial capillary electrophoresis (CE) instrumentation was developed, which enables handling sample volumes as little as 250nL for analytical applications where sample volume availability is of concern. Single-use micro-sampling inserts were prepared by thermal modification of polypropylene micropipette tips and the inserts were accommodated in standard CE vials in CE autosampler carousel. To ensure direct contact of separation capillary injection end with sample solution and to avoid possible damage to the capillary, a soft compression spring was placed at the bottom of the vial underneath the micro-sampling insert. Injections from sub-μL samples were carried out in conventional as well as in short-end injection mode, were compatible with standard i.d./o.d. (25-100μm/365μm) fused silica capillaries and with various background electrolyte solutions and detection modes. Excellent repeatability of replicate injections from 250nL to 3μL was achieved based on RSD values of quantitative analytical measures (peak heights ≤2.4% and peak areas ≤3.7%) for CE-UV-vis, CE-ESI-MS and CE-contactless conductivity detection of model basic drugs. The achieved RSD values were comparable with those for replicate injections of the drugs from standard CE vials. The reported concept of injections from micro-sampling inserts was further demonstrated useful in evaluation of micro-electromembrane extraction (μ-EME) of model basic drugs. Sub-μL volumes of operational solutions resulted in reduced lengths of μ-EME phases and improved extraction recoveries (66-91%) were achieved.
Fundamental operational principle and instrumental set-up of electromembrane extraction (EME) suggest that electrolysis may play an important role in this recently developed micro-extraction technique. In the present study, the effect of electrolysis in EME is described comprehensively for the first time and it is demonstrated that electrolysis considerably influences EME performance. Micro-electromembrane extraction (μ-EME) across free liquid membrane formed by 1-pentanol was utilized for real-time monitoring of the electrolytically induced changes in composition of μ-EME solutions. These changes were visualized with a set of acid-base indicators. Changes in colours of their aqueous solutions revealed serious variations in their pH values, which occurred within seconds to minutes of the μ-EME process. Variations of up to eight pH units were observed for indicator solutions initially prepared in 1, 5 and 10mM hydrochloric acid. No or only negligible pH changes (less than 0.15 pH unit) were observed for indicator solutions prepared in 50 and 100mM acetic acid demonstrating that initial composition of the aqueous solutions was the crucial parameter. These results were also confirmed by theoretical calculations of maximum pH variations in the solutions, which were based on total electric charge transfers measured in the μ-EME systems, and by exact measurements of their pH values after μ-EMEs. Acceptor solutions that, in the current practice, consist predominantly of low concentrations of strong mineral acids or alkali hydroxides may thus not always ensure adequate EME performance, which was manifested by decrease in extraction recoveries of a basic drug papaverine. A suitable remedy to the observed effects is the application of acceptor solutions containing high concentrations of weak acids or bases. These solutions not only eliminate the decrease in recoveries but also serve well as matrices of extracted samples for subsequent analysis by capillary electrophoresis.
- MeSH
- Chemistry Techniques, Analytical methods MeSH
- Electricity MeSH
- Electrolysis * MeSH
- Pharmaceutical Solutions MeSH
- Membranes, Artificial MeSH
- Liquid Phase Microextraction * MeSH
- Pentanols chemistry MeSH
- Solutions chemistry MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
A micro-electromembrane extraction (μ-EME) technique using electrically induced transfer of charged analytes across free liquid membranes (FLMs) was presented. A disposable extraction unit was proposed and it was made of a short segment of transparent perfluoroalkoxy tubing, which was successively filled with three liquid plugs serving as acceptor solution, FLM and donor solution. These plugs formed a three-phase extraction system, which was precisely defined, that was stable and required μL to sub-μL volumes of all respective solutions. Basic instrumental set-up and extraction principles of μ-EME were examined using an anionic and a cationic dye, 4,5-dihydroxy-3-(p-sulfophenylazo)-2,7-naphthalene disulfonic acid trisodium salt (SPADNS) and crystal violet, respectively. Transfers of the charged dyes from donor into acceptor solutions across FLMs consisting of 1-pentanol were visualized by a microscope camera and quantitative measurements were performed by UV-vis spectrophotometry. The effects of operational parameters of μ-EME system were comprehensively investigated and experimental measurements were accompanied with theoretical calculations. Extraction recoveries above 60% were achieved for 5min μ-EME of 1mM SPADNS at 100V with repeatability values below 5%. Selectivity of FLMs was additionally examined by capillary electrophoretic analyses of acceptor solutions and the potential of FLMs for μ-EME pretreatment of samples with artificial complex matrices was demonstrated.
- MeSH
- Anions chemistry MeSH
- Coloring Agents chemistry MeSH
- Electrophoresis, Capillary methods MeSH
- Cations chemistry MeSH
- Membranes, Artificial * MeSH
- Pentanols chemistry MeSH
- Reproducibility of Results MeSH
- Spectrum Analysis MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
This contribution describes properties and utilization of free liquid membranes (FLMs) in micro-electromembrane extraction (μ-EME) of analytes from samples with complex matrices. An FLM was formed as a plug of a selected organic solvent, 1-ethyl-2-nitrobenezene (ENB) or 2-nitrophenyloctyl ether, in a narrow bore polymeric tubing and was sandwiched between a plug of aqueous donor and aqueous acceptor solution. The FLM acted as a phase interface that enabled selective transfer of analytes from donor into acceptor solution. Acceptor solution after μ-EME was analysed by capillary electrophoresis (CE). Fundamental characteristics of FLMs were depicted and discussed by presenting experimental data on their performance for various basic operational parameters, such as composition and volume of donor/acceptor solution, applied extraction voltage, thickness of FLM and extraction time. Positively charged basic drugs (nortriptyline, haloperidol and loperamide) and their solutions in water, urine and blood serum served as model samples. It was shown that FLMs may offer fast, efficient and selective pretreatment of crude biological samples providing that basic operational parameters of μ-EME are set properly. At optimised conditions, basic drugs in 1.5μL of a biological sample were transferred across 1.5μL of FLM (ENB) into 1.5μL of acceptor solution in about 5min at an extraction voltage of 100V. Repeatability values of μ-EMEs and CE-UV analyses of the three basic drugs were better than 7.7% for peak areas, recoveries ranged between 19 and 52% and linear relationship was obtained for analytical signal vs. concentration in 1-50mgL(-1) range (r(2) better than 0.996). Limits of detection, defined as 3×S/N, were below 1mgL(-1) for all examined matrices.
- MeSH
- Electricity MeSH
- Electrophoresis, Capillary methods MeSH
- Pharmaceutical Preparations blood urine MeSH
- Humans MeSH
- Membranes, Artificial * MeSH
- Nitrobenzenes chemistry MeSH
- Solvents MeSH
- Solutions MeSH
- Water MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
