K Stulík

Charles University in Prague, Praha, Praha, Czech Republic

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Publications (76)253.38 Total impact

  • Petr Tůma, Karel Stulík
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    ABSTRACT: Capillary electrophoresis (CE) with contactless conductivity detection (C(4)D) is readily applicable to determinations of amino acids in clinical samples. Most of these analyses employ long separation pathways. This chapter describes CE/C(4)D determinations of 28 biogenic amino acids in a short capillary with an effective length of 18 cm. All the test amino acids can be mutually separated in electrolytes of 0.5-10 mol/L acetic acid. The time of analysis does not exceed 6 min; the limits of detection vary from 0.1 to 1.7 μmol/L for all the analytes. The pretreatment of the biological material is very simple, consisting of the removal of proteins by an addition of acetonitrile and subsequent filtration. The procedure has been successfully applied to determinations of the whole amino acid spectra in blood plasma, urine, saliva, cerebrospinal, and amniotic fluid samples.
    Methods in molecular biology (Clifton, N.J.) 01/2013; 919:13-23. · 1.29 Impact Factor
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    František Opekar, Petr Tůma, Karel Stulík
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    ABSTRACT: The paper provides a critical discussion of the present state of the theory of high-frequency impedance sensors (now mostly called contactless impedance or conductivity sensors), the principal approaches employed in designing impedance flow-through cells and their operational parameters. In addition to characterization of traditional types of impedance sensors, the article is concerned with the use of less common sensors, such as cells with wire electrodes or planar cells. There is a detailed discussion of the effect of the individual operational parameters (width and shape of the electrodes, detection gap, frequency and amplitude of the input signal) on the response of the detector. The most important problems to be resolved in coupling these devices with flow-through measurements in the liquid phase are also discussed. Examples are given of cell designs for continuous flow and flow-injection analyses and of detection systems for miniaturized liquid chromatography and capillary electrophoresis. New directions for the use of these sensors in molecular biology and chemical reactors and some directions for future development are outlined.
    Sensors 01/2013; 13(3):2786-801. · 2.05 Impact Factor
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    ABSTRACT: A fused silica capillary with a common outer diameter, 360 μm, but containing seven internal channels, each 28 μm in diameter (a multi-channel capillary), has been tested on electrophoretic separations of mixtures of dopamine, adrenaline and noradrenaline, using a contactless conductivity and UV photometric detection. It has been demonstrated that the sensitivity of the detection of these neurotransmitters in multi-channel capillary, in comparison with those obtained for a standard single-channel capillary with similar cross-sectional area, is comparable to that for the contactless conductivity and of about 50% higher for the UV photometry. The sensitivity is increased without loss of the separation efficiency, in contrast to UV detection with bubble cell. Further possibilities of using a multi-channel capillary are demonstrated on separations of mixtures of inorganic cations (K(+) , Ba(2+) , Na(+) , Mg(2+) , and Li(+) ) and mixtures of glucose and ribose. The main advantage off multi-channel capillary in comparison with a single-channel capillary with the same cross-sectional area becomes apparent in separations in background electrolytes of high conductivity.
    Electrophoresis 11/2012; · 3.26 Impact Factor
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    ABSTRACT: A capillary electrophoresis (CE) procedure with contactless conductivity detection (C(4)D) has been developed for monitoring of neutral mono- and disaccharides in drinks and foodstuffs. The separation of a mixture of seven neutral saccharides (glucose, fructose, galactose, mannose, ribose, sucrose and lactose) employed a quartz capillary, 5 μm i.d., with an effective length of 18.3 cm, and 75 mM NaOH (pH 12.8) as the background electrolyte (BGE). The limit of detection (LOD) values obtained lied within a range from 0.4 μmol L(-1) for lactose to 0.9 μmol L(-1) for ribose, with a separation time shorter than 140 s. The procedure was successfully applied to determinations of saccharides in fruit juices, Coca-Cola, milk, red and white wines, yoghurts, honey and a foodstuff additive.
    Analytica chimica acta 07/2011; 698(1-2):1-5. · 4.31 Impact Factor
  • František Opekar, Karel Stulík
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    ABSTRACT: Analyses of very complex samples involving capillary and chip electrophoresis often require dual (multiple) detection to attain sufficient selectivity of determination. The present work reviews and critically evaluates selected combinations of electrochemical detection techniques among themselves and with absorption spectrometric, fluorescence and luminescence techniques. Amperometry, contact and contactless conductometry, UV photometry and fluorescence measurements are paid special attention. Some information is also given on combinations of spectrometric techniques with mass spectrometry. The properties of the detection systems are critically discussed, examples are illustrated in figures and some details on the characteristics of dual detectors and their applications are tabulated.
    Electrophoresis 03/2011; 32(8):795-810. · 3.26 Impact Factor
  • Petr Tůma, Eva Samcová, Karel Stulík
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    ABSTRACT: A mixture of 29 organic acids (OAs) occurring in urine was analyzed by capillary electrophoresis (CE) with capacitively coupled contactless conductivity detection (C(4)D) and UV photometric detection. The optimized analytical system involved a 100 cm long polyacrylamide-coated capillary (50 μm i.d.) and the background electrolyte of 20mM 2-morpholinoethanesulfonic acid (MES)/NaOH+10% (v/v) methanol, pH 6.0 (pH is related to the 20mM MES/NaOH buffer in water). The LOD values obtained by C(4)D for the OAs which do not absorb UV radiation range from 0.6 μM (oxalic acid) to 6.8 μM (pyruvic acid); those obtained by UV photometry for the remaining OAs range from 2.9 μM (5-hydroxy-3-indoleacetic acid) to 10.2 μM (uric acid). The repeatability of the procedure developed is characterized by the coefficients of variation, which vary between 0.3% (tartaric acid) and 0.6% (5-hydroxy-3-indoleacetic acid) for the migration time and between 1.3% (tartaric acid) and 3.5% (lactic acid) for the peak area. The procedure permitted quantitation of 20 OAs in a real urine sample and was applied to monitoring of the occurrence of the inborn metabolic fault of methylmalonic aciduria.
    Analytica chimica acta 01/2011; 685(1):84-90. · 4.31 Impact Factor
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    ABSTRACT: A very simple and readily performed method is described for the preparation of poly(styrene-divinylbenzene-methacrylic acid) monolithic columns for capillary liquid chromatography. The effect of the methacrylic acid content on the morphological and chromatographic properties has been investigated. Methacrylic acid is shown to be essential for isocratic separations of small organic analytes by capillary liquid chromatography. Column efficiencies of about 28,000 theoretical plates/m have been obtained for all the test compounds. The batch-to-batch and run-to-run repeatability of the retention times is better than 1.5%.
    Journal of Chromatography A 01/2011; 1218(11):1544-7. · 4.61 Impact Factor
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    ABSTRACT: In proteomics, proteins can be identified by enzymatic cleavage of the target protein using an enzyme of the known specificity (primarily trypsin), sequencing the obtained specific peptides by MS and comparing the amino acid sequence of the peptides with a protein database. The sophisticated approach described above was used in this study to determine and verify the original species of cheeses. Proteins were extracted from three different cheese samples which were produced from cow, sheep and goat milks. The isolated proteins were cleaved with trypsin and the peptides obtained were sequenced and identified by a HPLC-chip/MS/MS microfluidic system. Two different extraction methods and two various chromatographic sorbents packed in plastic chips were studied. Beta-lactoglobulin and four kinds of casein were found in the cheese samples. The species of kappa-casein were identified unambiguously in all the three cheese samples and, thus, kappa-casein can be used to determine the origin of milk of the cheese. The other proteins found in the samples show very similar primary structures and cannot be recommended for identification of the cheese milk origin.
    Journal of Separation Science 08/2010; 33(16):2515-9. · 2.59 Impact Factor
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    ABSTRACT: CE with contactless conductivity detection has been used to separate 28 biogenic amino acids in a short capillary with an effective length of 18 cm. All the tested amino acids can be mutually separated in 0.5-10 mol/L acetic acid electrolytes. The time of analysis does not exceed 6 min and the LODs vary from 0.1 to 1.7 micromol/L. The CVs lie within the intervals 0.01-0.4% and 0.9-4% for the migration times and the analyte peak areas, respectively. The procedure has been successfully applied to the determinations of the whole amino acid spectra in blood plasma, urine, saliva and cerebrospinal fluid samples.
    Journal of Separation Science 08/2010; 33(16):2394-401. · 2.59 Impact Factor
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    ABSTRACT: A CE procedure employing capacitively coupled contactless conductivity detection has been developed for direct determination of the glycerol and mannitol polyalcohols in biological and pharmacological samples. Both glycerol and mannitol are fully separated from the sample matrix within very short times of 3.0 and 3.9 min, respectively, when using the optimized BGE, 60 mM H3BO3+30 mM LiOH (pH 9.1). The LODs amount to 0.5 microM for glycerol and 0.3 microM for mannitol. The repeatability of the glycerol determination in real biological materials is characterized by the coefficient of variation values, 0.5 and 3.2%, for the migration time and the peak area, respectively. The procedure has been used to monitor the free glycerol concentration in adipose tissue microdialyzates. A physiological study has demonstrated that the lipolysis occurring during a sporting action can be stimulated by local application of adrenaline. The procedure has further been utilized to determine mannitol in a pharmacological preparation.
    Electrophoresis 06/2010; 31(12):2037-43. · 3.26 Impact Factor
  • Frantisek Opekar, Karel Stulik
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 01/2010; 30(26).
  • J Míka, F Opekar, P Coufal, K Stulík
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    ABSTRACT: The design is described of a thin-layer contactless conductivity detector suitable for liquid chromatography and flow-injection analysis. Its principal analytical parameters have been determined using a potassium chloride solution: the linear dynamic range extends from 7.5 x 10(-6) to 1.5 x 10(-2) S m(-1), corresponding to the KCl concentration range from 0.5 to 1000 microM, the limit of detection equals 3.5 x 10(-6) S m(-1) (0.2 microM KCl), the detection repeatability, expressed in terms of the relative standard deviation, amounts to 1.13% and the detection volume is 0.6 microL. The detector was applied to detection of ionic compounds, benzoic, lactic and octanesulfonic acids, and sodium capronate, after their separation by liquid chromatography in a Biospher PSI 100C 18 columns using a 60% aqueous acetonitrile mobile phase. The frequency characteristics of the detector are reasonably theoretically described on the basis of a simple model which is commonly used in the field of contactless impedance detectors.
    Analytica chimica acta 10/2009; 650(2):189-94. · 4.31 Impact Factor
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    ABSTRACT: CE with contactless conductivity detection has been used to determine the glycine neurotransmitter in periaqueductal gray matter (PAG) of rats. The LOD for glycine has been decreased to a value of 0.2 microM by adding 75% v/v of ACN to the samples and increasing the sample zone introduced to a value of 20% of the overall capillary length. The repeatabilities of the analyte migration times and the zone areas amount to 2.1 and 2.7%, respectively. The optimized CE/contactless conductivity detection method makes it possible to determine the micromolar concentrations of glycine in PAG microdialyzates without the necessity of sample derivatization. It follows from a pharmacological study that a local inflammation initiated by an application of carrageenan increased the glycine concentration in the rat PAG seven times, compared with a control. The glycine level in PAG can be decreased and the pain suppressed by administering paracetamol.
    Electrophoresis 09/2009; 30(19):3436-41. · 3.26 Impact Factor
  • Frantisek Opekar, Pavel Coufal, Karel Stulík
    Chemical Reviews 07/2009; 109(9):4487-99. · 41.30 Impact Factor
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    ABSTRACT: The approaches to the analysis for estrogen compounds as environmental pollutants are critically reviewed and evaluated on the basis of significant, recent original publications. The importance of sample pretreatment and analyte preconcentration techniques is pointed out, with an emphasis on SPE and on the use of highly selective interactions such as molecular recognition. The hyphenated systems of high-performance gas or liquid chromatography and mass spectrometric techniques are discussed as the basic methods of determination of estrogens in environmental samples. Immunochemical procedures are shown to be useful in semiquantitative screening of estrogen pollutants (e.g. ELISA kits). Classical HPLC and GC with common UV/Vis, fluorescence and electrochemical detection are useful in routine checking on higher pollutant concentrations.
    Journal of Separation Science 03/2009; 32(5-6):867-82. · 2.59 Impact Factor
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    ABSTRACT: A GC/MS procedure has been developed, optimized, and applied to characterization of oil binders in paintings. The procedure involves hydrolysis of lipids to fatty acids (FAs) and derivatization of FAs to fatty acid methyl esters (FAMEs) by a solution of sodium methanolate in methanol at an elevated temperature. FAMEs are analyzed by temperature-programed GC followed by full-scan MS. Old and dried samples are subjected to extraction of nonpolymerized FAMEs into dichloromethane prior to hydrolysis. The method provides a good repeatability of results and has been applied to the characterization of common plant oils used in paintings, to commercial oil and tempera paints, to model painting samples, and to samples taken from real paintings. The fresh oils and binders can readily be identified and characterized. The ratio of the methyl esters of palmitic and stearic acids can be used to characterize oil binders in old works of art.
    Journal of Separation Science 05/2008; 31(6-7):1067-73. · 2.59 Impact Factor
  • Pavel Coufal, Vera Pacáková, Karel Stulík
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    ABSTRACT: This review points out some important trends in the development of the detection techniques for small ions in CE. On the basis of selected literature references it briefly discusses some general requirements on detection techniques in CE. Various optical measurements, mass spectrometric approaches and electrochemical detection techniques are dealt with. Some specific features of microchip CE separation and detection are pointed out and possibilities of dual detection are mentioned. The principal parameters of the above detection techniques are then briefly compared.
    Electrophoresis 11/2007; 28(19):3379-89. · 3.26 Impact Factor
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    ABSTRACT: CE with capacitively coupled contactless detection (C4D) was used to determine 3-methylhistidine (3-MH) and 1-methylhistidine (1-MH). The C4D response to 3-MH was studied in a BGE consisting of 500 mM acetic acid and ammonia at varying concentration and the results were compared with the theory. Complete separation of a model mixture of 3-MH, 1-MH, and histidine (His) was attained in two optimized BGEs, one containing 500 mM HAc, 20 mM NH4OH, and 0.1 % m/v hydroxyethylcellulose (HEC), pH 3.4 (I) and the other consisting of 100 mM morpholinoethanesulfonic acid (MES), 25 mM LiOH, and 0.1 % m/v HEC, pH 5.5 (II). These optimized BGEs were tested in CE/C4D analyses of urine. Promising results were obtained for separation and determination of 3-MH, 1-MH, and His on a silicon microchip, using aluminum strips as the C4D electrodes; the three analytes were baseline-separated within less than 30 s with a separation channel effective length of 38 mm. The LOD were satisfactory and amounted to 26.4 microM for 3-MH and 18.3 microM for 1-MH.
    Electrophoresis 08/2007; 28(13):2174-80. · 3.26 Impact Factor
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    ABSTRACT: Two chromatographic methods have been compared for analysis of protein-binding media used in paintings, namely, HPLC with fluorescence detection and GC-MS. The proteins were hydrolyzed to the corresponding amino acids (AAs) by gaseous HCl and the AAs were derivatized with methyl chloroformate, followed by GC-MS or by HPLC after derivatization with the AccQ fluorescence reagent. The hydrolysis, derivatization reactions and the chromatographic procedures have been optimized and applied to standard binding media, model and real samples of paintings. The methods have been compared and critically evaluated.
    Journal of Separation Science 12/2006; 29(17):2653-63. · 2.59 Impact Factor
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    ABSTRACT: This review briefly summarizes the present state of the preparation and use of capillary monolithic columns for liquid chromatography (LC) and electrochromatography (EC). Most important approaches to the preparation of monolithic stationary phases based on organic polymers are outlined and the properties of the monoliths obtained are compared with those of classical particulate phases. A few selected applications of monolithic columns are shown to demonstrate the most important advantages of monolithic capillary columns. It is concluded that both the monolithic and particulate capillary columns are important and that judicious choice of the type suitable for a particular application requires careful consideration of the purpose of the separation and the properties of the solutes to be separated. Monolithic columns are substantially younger than packed ones and thus will require further theoretical and experimental study to further improve their preparation and to enable reliable prediction of their properties and applicability; nevertheless, they are very promising for the future.
    Journal of Chromatography B 10/2006; 841(1-2):79-87. · 2.49 Impact Factor

Publication Stats

435 Citations
253.38 Total Impact Points

Institutions

  • 1972–2013
    • Charles University in Prague
      • • Department of Analytical Chemistry (PF)
      • • Ústav biochemie, buněčné a molekulární biologie - oddělení buněčné a molekulární biologie (3. LF)
      Praha, Praha, Czech Republic
  • 2004
    • Academy of Sciences of the Czech Republic
      • Ústav chemických procesů
      Praha, Hlavni mesto Praha, Czech Republic
  • 1992
    • Institute of Inorganic Chemistry
      Aussig, Ústecký, Czech Republic