Micro-electromembrane extractions (μ-EMEs) across free liquid membranes (FLMs) were applied to simultaneous extractions of anions and cations. A transparent narrow-bore polymeric tubing was filled with adjacent plugs of μL volumes of aqueous and organic solutions, which formed a stable five-phase μ-EME system. For the simultaneous μ-EMEs of anions and cations, aqueous donor solution was the central phase, which was sandwiched between two organic FLMs and two aqueous acceptor solutions. On application of electric potential, anions and cations in the donor solution migrated across the two FLMs and into the two peripheral acceptor solutions in the direction of anode and cathode, respectively. Visual monitoring of anionic (tartrazine) and cationic (phenosafranine) dye confirmed their simultaneous μ-EMEs and their rapid (in less than 5 min) transfers into anolyte and catholyte, respectively. The concept of simultaneous μ-EMEs was further examined with selected model analytes; KClO4 was used for μ-EMEs of inorganic anions and cations and ibuprofen and procaine for μ-EMEs of acidic and basic drugs. Quantitative analyses of the resulting acceptor solutions were carried out by capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C(4)D). Good extraction recoveries (91-94%) and repeatability of peak areas (≤6.3%) were achieved for 5 min μ-EMEs of K(+) and ClO4(-). Extraction recoveries and repeatability of peak areas for 5 min μ-EMEs of ibuprofen and procaine were also satisfactory and ranged from 35 to 63% and 7.6 to 11.3%, respectively. Suitability of the presented micro-extraction procedure was further demonstrated on simultaneous μ-EMEs with subsequent CE-C(4)D of ibuprofen and procaine from undiluted human urine samples.

• Klíčová slova
• Drugs, Free liquid membranes, Inorganic ions, Micro-electromembrane extractions, Simultaneous extractions,
• MeSH
• anionty izolace a purifikace   MeSH
• barvicí látky izolace a purifikace   MeSH
• elektroforéza kapilární MeSH
• kationty izolace a purifikace   MeSH
• membrány umělé * MeSH
• referenční standardy MeSH
• roztoky MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• anionty MeSH
• barvicí látky MeSH
• kationty MeSH
• membrány umělé * MeSH
• roztoky 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.

• Klíčová slova
• Basic drugs, Capillary electrophoresis, Complex samples, Free liquid membranes, Micro-electromembrane extraction,
• MeSH
• elektřina MeSH
• elektroforéza kapilární metody   MeSH
• ethery MeSH
• léčivé přípravky krev   moč   MeSH
• lidé MeSH
• membrány umělé * MeSH
• nitrobenzeny chemie   MeSH
• rozpouštědla MeSH
• roztoky MeSH
• voda MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• 1-ethyl-2-nitrobenezene MeSH Prohlížeč
• 2-nitrophenyl octyl ether MeSH Prohlížeč
• ethery MeSH
• léčivé přípravky MeSH
• membrány umělé * MeSH
• nitrobenzeny MeSH
• rozpouštědla MeSH
• roztoky MeSH
• voda MeSH

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.

• Klíčová slova
• Electrolysis, Electromembrane extractions, Free liquid membranes, Micro-electromembrane extractions, Supported liquid membranes,
• MeSH
• chemické techniky analytické metody   MeSH
• elektřina MeSH
• elektrolýza * MeSH
• lékové roztoky MeSH
• membrány umělé MeSH
• mikroextrakce kapalné fáze * MeSH
• pentanoly chemie   MeSH
• roztoky chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• lékové roztoky MeSH
• membrány umělé MeSH
• n-pentanol MeSH Prohlížeč
• pentanoly MeSH
• roztoky MeSH

Manual handling of microliter volumes of samples and reagents is usually prone to errors and may have direct consequence on the overall performance of microextraction process. Direct connection of a syringe pump and a disposable microextraction unit using flexible polymeric tubing was employed for semi-automated liquid handling in micro-electromembrane extraction (μ-EME). A three-phase μ-EME system was formed by consecutive withdrawal of microliter volumes of donor solution, free liquid membrane (FLM) and acceptor solution into the unit. Excellent repeatability and accuracy of the withdrawal sequence was achieved for solution volumes typically used in μ-EME (1-5 μL) as well as excellent correlation between the initially withdrawn and the finally collected solution volumes. μ-EMEs were initiated by application of d.c. electric potential to the terminal aqueous solutions and specific μ-EME parameters were optimized in order to ensure complete transfer of model analytes from donor to acceptor solution. Exhaustive μ-EMEs of three basic drugs, nortriptyline, papaverine and haloperidol, were achieved from 1.3 μL of acidified donor solution (10 mM HCl) across 2.5 μL of FLM (1-ethyl-2-nitrobenzene) into 1.3 μL of acidified acceptor solution (25 mM HCl) in 10 min at 150 V. The three drugs were also exhaustively extracted from salt- and protein-containing standard solutions, human urine and human plasma with extraction recoveries ranging from 79 to 102%. Resulting acceptor solutions were analysed by capillary electrophoresis with ultraviolet detection (CE-UV) and the μ-EME-CE-UV method was characterized by good linearity (coefficients of determination ≥ 0.992), high repeatability (RSD values ≤ 6.5%) and limits of detection ≤ 0.15 mg/L.

• Klíčová slova
• Automation, Basic drugs, Body fluids, Exhaustive extraction, Free liquid membrane, Micro-electromembrane extraction,
• MeSH
• chemická frakcionace přístrojové vybavení   MeSH
• design vybavení MeSH
• elektřina MeSH
• elektrody MeSH
• elektroforéza kapilární MeSH
• léčivé přípravky krev   izolace a purifikace   moč   MeSH
• lidé MeSH
• membrány umělé * MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• léčivé přípravky MeSH
• membrány umělé * MeSH

This work investigated selective micro-electromembrane extractions (μ-EMEs) of the colored indicators metanil yellow and congo red (visual proof-of-principle) and the small drug substances nortriptyline, papaverine, mianserin, and citalopram (model analytes) based on their acid-base strength. With two free liquid membranes (FLMs), the target analytes were extracted from aqueous donor solution, across FLM 1 (1-pentanol, 1-ethyl-2-nitrobenzene (ENB) or 4-nitrocumene (4-NC)), into aqueous acceptor solution 1, further across FLM 2 (1-pentanol, ENB or 4-NC), and finally into aqueous acceptor solution 2. All phases had volumes between 1.0 and 1.5 μL and extractions were promoted by 200-300 V d.c. applied across the five-phase μ-EME system formed in a perfluoroalkoxy capillary tubing. The anode was located in acceptor solution 2 and the cathode was located in donor solution for μ-EMEs of acidic analytes, and locations of the electrodes were vice versa for μ-EMEs of basic analytes. After μ-EME, donor solution and acceptor solution 1 and 2 were analyzed by capillary electrophoresis or liquid chromatography-mass spectrometry. The model analytes migrated efficiently in the proposed μ-EME system, their migration behavior was controlled by pH in aqueous solutions and their selective fractionation into acceptor solution 1 and 2 was demonstrated based on their acid-base strength. Under optimal conditions, acceptor solution 2 contained 60% nortriptyline (pKa = 10.5) and less than 1% papaverine (pKa = 6.0) and acceptor solution 1 contained 17% nortriptyline and 27% papaverine after 15 min of μ-EME. The five-phase μ-EME system was also compatible with human plasma samples. Work is in progress to further increase the fractionation capability, and to implement the concept into microfluidic platforms.

• Klíčová slova
• Acid-base indicators, Basic drugs, Extraction selectivity, Free liquid membranes, Micro-electromembrane extraction, Plasma samples,
• MeSH
• acidobazická rovnováha MeSH
• chromatografie kapalinová MeSH
• hmotnostní spektrometrie MeSH
• koncentrace vodíkových iontů MeSH
• membrány umělé * MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• membrány umělé * 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.

• Klíčová slova
• Capillary electrophoresis, Contactless conductivity detection, Mass spectrometry, Micro-extractions, Micro-sampling, UV–vis detection,
• MeSH
• elektroforéza kapilární přístrojové vybavení   metody   MeSH
• elektrolyty chemie   MeSH
• hmotnostní spektrometrie MeSH
• nortriptylin analýza   izolace a purifikace   MeSH
• papaverin analýza   MeSH
• roztoky chemie   MeSH
• spektrofotometrie ultrafialová MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• elektrolyty MeSH
• nortriptylin MeSH
• papaverin MeSH
• roztoky MeSH

Preconcentration potential of micro-electromembrane extraction (μ-EME) across free liquid membrane (FLM) was examined with an anionic and a cationic dye, 4,5-dihydroxy-3-(p-sulfophenylazo)-2,7-naphthalene disulfonic acid, trisodium salt (SPADNS) and phenosafranine, respectively. For the first time, it was shown that the spatial flexibility of FLMs enabled application of tailored extraction units with mutually different shapes and migration cross-sections for FLMs, donor and acceptor solutions. Thus, e.g. conical units enabled easy and reproducible formation of a three-phase extraction system (donor/FLM/acceptor) with sub-μL volumes of acceptor solutions as well as rapid and highly efficient preconcentration of the two dyes. Quantitative measurements of resulting solutions were carried out by UV-vis spectrophotometry and enrichment factors of up to 98 were achieved for μ-EMEs of 20 μM SPADNS (50 μL) preconcentrated into 0.5 μL of pure water across 1-pentanol at -150 V for 18 min. Visual monitoring of the entire extraction process (with USB microscope camera) was possible across transparent extraction units, moreover, important extraction parameters, such as FLM dimensions and donor-to-acceptor solution volume ratio, which determine the mechanical stability of the membrane and maximum enrichment factor, respectively, were readily adjusted. Combination of μ-EME across FLMs with capillary electrophoresis (CE) was further shown suitable for preconcentration and determination of perchlorate in drinking water samples. Good repeatability of the μ-EME-CE method (RSD values better than 9.5%), linear relationship for the analytical signal vs. concentration (r(2) better than 0.997) and enrichment factors of up to 30 were achieved for μ-EMEs of perchlorate across 1-pentanol and 1-hexanol based FLMs.

• Klíčová slova
• Capacitively coupled contactless conductivity detection, Capillary electrophoresis, Free liquid membranes, Micro-electromembrane extraction, Preconcentration, UV–vis spectrophotometry,
• Publikační typ
• časopisecké články 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.

• Klíčová slova
• Free liquid membranes, Micro-electromembrane extraction, SPADNS, UV–vis spectrophotometry,
• MeSH
• anionty chemie   MeSH
• barvicí látky chemie   MeSH
• elektroforéza kapilární metody   MeSH
• kationty chemie   MeSH
• membrány umělé * MeSH
• pentanoly chemie   MeSH
• reprodukovatelnost výsledků MeSH
• spektrální analýza MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• anionty MeSH
• barvicí látky MeSH
• kationty MeSH
• membrány umělé * MeSH
• n-pentanol MeSH Prohlížeč
• pentanoly MeSH

A novel approach for automation of Micro-Extraction by Packed Sorbent (MEPS), a solid phase extraction technique, is presented, enabling precise and repeatable liquid handling due to the employment of sequential injection technique. The developed system was used for human urine sample clean-up and pre-concentration of betaxolol before its separation and determination. A commercial MEPS C-18 cartridge was integrated into an SIChrom™ system. The chromatographic separation was performed on a monolithic High Resolution C18 (50×4.6 mm) column which was coupled on-line in the system with Micro-Extraction using an additional selection valve. A mixture of acetonitrile and aqueous solution of 0.5% triethylamine with acetic acid, pH adjusted to 4.5 in ratio 30:70 was used as a mobile phase for elution of betaxolol from MEPS directly onto the monolithic column where the separation took place. Betaxolol was quantified by a fluorescence detector at wavelengths λ(ex)=220 nm and λ(em)=305 nm. The linear calibration range of 5-400 ng mL(-1), with limit of detection 1.5 ng mL(-1) and limit of quantification 5 ng mL(-1) and correlation r=0.9998 for both the standard and urine matrix calibration were achieved. The system recovery was 105±5%; 100±4%; 108±1% for three concentration levels of betaxolol in 10 times diluted urine - 5, 20 and 200 ng mL(-1), respectively.

• Klíčová slova
• Automation, Betaxolol, Fluorimetry, Liquid chromatography, Micro-Extraction by Packed Sorbent (MEPS), Sequential Injection Chromatography (SIC),
• MeSH
• analýza moči přístrojové vybavení   metody   MeSH
• betaxolol izolace a purifikace   moč   MeSH
• chromatografie metody   MeSH
• design vybavení MeSH
• fluorescenční spektrometrie MeSH
• injekce * MeSH
• lidé MeSH
• mikroextrakce na pevné fázi metody   MeSH
• Check Tag
• lidé MeSH
• mužské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• betaxolol MeSH

A novel approach of head-space single-drop micro-extraction applied to the determination of ethanol in wine is presented. For the first time, the syringe of an automated syringe pump was used as an extraction chamber of adaptable size for a volatile analyte. This approach enabled to apply negative pressure during the enrichment step, which favored the evaporation of the analyte. Placing a slowly spinning magnetic stirring bar inside the syringe, effective syringe cleaning as well as mixing of the sample with buffer solution to suppress the interference of acetic acid was achieved. Ethanol determination was based on the reduction of a single drop of 3mmol L(-1) potassium dichromate dissolved in 8mol L(-1) sulfuric acid. The drop was positioned in the syringe inlet in the head-space above the sample with posterior spectrophotometric quantification. The entire procedure was carried out automatically using a simple sequential injection analyzer system. One analysis required less than 5min including the washing step. A limit of detection of 0.025% (v/v) of ethanol and an average repeatability of less than 5.0% RSD were achieved. The consumption of dichromate reagent, buffer, and sample per analysis were only 20μL, 200μL, and 1mL, respectively. The results of real samples analysis did not differ significantly from those obtained with the references gas chromatography method.

• Klíčová slova
• Ethanol, Head-space, In-syringe, Sequential injection analysis, Single-drop micro-extraction, Spectrophotometric detection,
• MeSH
• automatizace * MeSH
• ethanol analýza   MeSH
• průtoková injekční analýza * přístrojové vybavení   MeSH
• velikost částic MeSH
• víno analýza   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• ethanol MeSH