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P Bocek

Publications and source records attributed to P Bocek.

At least 73 records · Page 4Linked to original sources
PubMed1995

Theory of zone separation in isotachophoresis: a diffusional approach.

The qualitative characteristics of isotachophoresis differ substantially from "classical" separation methods such as chromatography or zone electrophoresis. Self-sharpening zone boundaries and step-like concentration profiles are the most specific features of this method, which does not allow the description of the isotachophoretic separation in usual "chromatographic" terms, such as resolution or number of theoretical plates. A theory is presented in this paper, combining the usual isotachophoretic separation characteristics with the theory of isotachoporetic zone boundary, which is the only element of the isotachophoretic system with dispersional properties. This allows us to consider situations near the limits of the isotachophoretic method as far as both selectivity and sample amount (i.e., zone size) are concerned. Based on a simplified expression of the concentration profiles across the isotachophoretic zone boundary, separation and separation limits are described and discussed in terms of resolution, selectivity and zone capacity. Equations are derived showing the relationships between resolution, boundary width, selectivity, sample amount, and column and electrolyte conditions. A simple phenomenological equation is presented, expressing isotachophoretic resolution as a function of only sample amount (or sample zone length) and boundary width. A thermodynamic form of this equation is derived, which is shown to be similar to such an expression for resolution in zone electrophoresis. In both cases resolution is a function of sample selectivity, electric field strength and column length. A simple theoretical model for zone capacity is presented, making it possible to estimate the separation performance of isotachophoretic systems. Based on the presented theory, parallels between isotachophoresis and zone electrophoresis are discussed and both methods are compared.

Diffusion↗
PubMed1995

Sample self-stacking and sample stacking in zone electrophoresis with major sample components of like charge: general model and scheme of possible modes.

A theoretical study is presented of zone electrophoretic behavior of samples that contain one or more minor analytes and at least one major ionogenic component of like charge. Based on a simple model comprising weak univalent anionic electrolytes, conditions are derived under which analytes are temporarily focused isotachophoretically into very narrow zones by a sample self-stacking effect provided by the major sample components. Requirements for minimal/maximal mobility and a background coion concentration dependent minimal concentration of a major sample component (stacker) are presented. For systems in which sample self-stacking does not apply, an expression for the concentrating factor is derived that involves the effects of both nonselective (classical) and selective sample stacking, the latter being a consequence of electrophoretic separation of the minor analyte from the major component. The theory derived is discussed with selected model examples by using both numerical calculation and computer simulation.

Electric Conductivity↗
PubMed1995

An improvement of restriction analysis of bacteriophage DNA using capillary electrophoresis in agarose solution.

Seven representatives of the serogroup B Staphylococcus aureus bacteriophages, 29, 53, 55, 83A, 85, phi 11 and 80 alpha, were examined by capillary electrophoresis (CE) for genomic homology using DNA restriction analysis. Genomic DNA of individual bacteriophages was cleaved by HindIII restriction endonuclease, and the resulting restriction fragments were separated by standard horizontal agarose slab gel electrophoresis (SGE) as well as by CE in low-melting-point agarose solutions. The number and size of restriction fragments identified by both methods were compared. The high separation power of CE makes it possible to extend the restriction fragment patterns. In most of the restriction patterns, some additional restriction fragments as small as 150 bp, not identified by SGE, were detected. With respect to speed, high separation efficiency, low sample consumption and automation, CE offers a simple procedure for processing of multiple samples cost-effectively in a reasonable time. The comparison of the complemented restriction patterns of the different phage strains and the subsequent identification of their common fragments leads to a deeper understanding of their phylogenetic relationships. The genome homologies expressed for individual phage pairs in terms of coefficient F values ranged from 15 to 69%. These values are in good accordance with the degree of DNA homology of these phages as determined by DNA hybridization studies and thermal denaturation analysis of DNA by other authors. The total size of each phage genome was estimated by adding the sizes of individual restriction fragments.

Bacteriophages↗
PubMed1994

Chiral separations by capillary electrophoresis: present state of the art.

Capillary electrophoresis is a powerful tool for chiral separation of ionogenic enantiomers in solutions. This article brings an overview of the theory of electrophoretic separations with special emphasis on enantiomer-chiral selector equilibria, followed by a survey of indirect separations, based on formation of diastereomers with different electrophoretic mobilities, and a comprehensive appraisal of direct separations when the chiral recognition stems from (i) host-guest interactions using cyclodextrins and crown ethers as hosting agents, (ii) ligand exchange mechanism, (iii) affinity interactions or (iv) a combination of solute-chiral selector interactions with micellar electrophoretic transport. Finally, some trends in chiral separations by capillary electrophoresis are discussed.

Cyclodextrins↗
PubMed1994

Consequences of a maximum existing in the dependence of separation selectivity on concentration of cyclodextrin added as chiral selector in capillary zone electrophoresis.

The maximum in the dependence of the separation selectivity on the concentration of cyclodextrin may be utilized for the determination of the mean value of host-guest interaction constants of the separated enantiomers. For the hosting of N-t-BOC-DL-tryptophan by beta-cyclodextrin, the mean value of these constants, found by drop line estimated from the cyclodextrin concentration corresponding at the maximum, is 350 L.mol-1. The separation at this concentration of cyclodextrin offers the highest resolution in the shortest separation time. It is shown that commonly used simple preliminary experiments, testing the capability of a cyclodextrin to resolve chiral compounds, and based on relatively high cyclodextrin concentrations, may easily lead to incorrect conclusions in cases of enantiomers strongly interacting with the cyclodextrin used.

Cyclodextrins↗
PubMed1994

Capillary zone electrophoresis with indirect photometric detection in the visible range.

Sensitivity and applicability of commonly used indirect photometric detection in the UV region can be adversely affected by the absorption of the UV light by detected solutes and/or by matrix constituents migrating with them. If the visible light is exploited instead of the UV light, both these disadvantages may be for the most part eliminated, and, moreover, the indirect photometric detection will extend its versatility and sensitivity. Prospects as well as main problems of the approach were tested using inorganic ions as analytes. If organic dyes with a molar light absorption coefficient of the order of 10(6) mol-1 L m-1 was selected as the light-absorbing constituents of the background electrolyte, detection sensitivity comparable with the best reported results was reached for anions; for cations, the detection limit was even lower by two orders of magnitude.

Anions↗
PubMed1993

Cloning and sequence of the cDNA coding for rat type II Fc gamma receptor of mast cells.

A clone encoding the rat type II Fc gamma receptor was isolated from a cDNA library of the rat mucosal mast cell line RBL-2H3 and its sequence determined. The predicted amino acid sequence is highly homologous with the mouse type II as well as rat type III Fc gamma receptors. The site of alternative splicing which generates the mouse Fc gamma Rb2 isoform is completely conserved. Hence we consider the new sequence to encode a rat Fc gamma RII b2 isoform. In further analogy to the mouse receptor, no consensus motif known to be involved in accessory chain association was observed in the transmembranal domain. The importance of the identification of this receptor for investigation of the immunological stimulation of mast cells is discussed.

Amino Acid Sequence↗
PubMed1993

[Fertility in patients treated for malignant tumors before puberty].

35 patients with malignant tumours were examined. In 4 of them comprehensive therapy was initiated in the course of the first five years of life. In the remaining 31 cases the first symptoms of the disease appeared between the ages of 9 to 16 years. In the entire group spermiogenic function was insufficient in about 65% of the afflicted. Subnormal values of plasma testosterone were found only in 9%.

Adolescent↗
PubMed1991

Theoretical background for clinical and biomedical applications of electromigration techniques.

This review presents the theoretical principles of analytical electrophoresis. The basic rules which control the movement of ionic species in electrostatic fields, together with the phenomenological theory of the resulting mass transport are analysed. The separation principles and capabilities of zone electrophoresis, isotachophoresis, isoelectric focusing, micellar electrokinetic chromatography and gel electrophoresis are evaluated. The most important effects accompanying electrophoresis, such as the production of Joule heat, electroosmosis and diffusion are discussed.

Chemical Phenomena↗
PubMed1991

Determination of halofuginone in feedstuffs by the combination of capillary isotachophoresis and capillary zone electrophoresis in a column-switching system.

A method has been developed for the determination of the coccidiocidic drug halofuginone in feedstuff concentrates which is based on the combination of capillary isotachophoresis and capillary zone electrophoresis in the column-switching mode. The high load capacity of the isotachophoretic step and high sensitivity of the zone electrophoretic step enabled analysis of up to 25 microliters of sample solution containing as little as 10(-8) M halofuginone with excellent reproducibility (R.S.D. about 1%). Attention was paid to the possibility of the existence of transient local isotachophoresis in the zone electrophoretic step, and experimental and theoretical methods of revealing zones migrating isotachophoretically in the background electrolyte were shown.

Animal Feed↗
PubMed1991

Electrophoretic size separations in liquified agarose of polystyrene particles and circular DNA.

Polystyrene sulfate particles of 0.37 to 1.78 mu in diameter are retarded in their electrophoretic migration in proportion to the concentration of agarose liquified above its gelling temperature. In the concentration range of 0.02 to 0.2% liquified agarose, the degree of this retardation in electrophoresis at 40 degrees C is inversely related to particle size. By contrast, mitochondrial DNA (16 kb), plasmid pBR322 DNA (4 kb) and plasmid PSA509 DNA (3 kb) exhibit under the same conditions a degree of retardation which is proportional to their size. This confirms the existence of two divergent mechanisms of size separation similarly observed in other liquid polymer media, i.e. one based on collisions with the gel fiber (molecular sieving) and one based on exclusion from the fiber network (the electrophoretic equivalent of gel permeation).

DNA, Circular↗
PubMed1991

Pressure refilled polyacrylamide columns for the separation of oligonucleotides by capillary electrophoresis.

The separation of oligonucleotides by capillary zone electrophoresis (CZE) was studied in fused silica separation capillaries filled by linear (noncrosslinked) polyacrylamide (PAA) solutions, introduced into the capillary from the stock by pressure after each analysis. The time-consuming in-capillary polymerization step could thus be avoided, and fast and reproducible repetition of the analyses was assured. The PAA concentrations varied within the range of 3-10% and both the reproducibility of the analyses and the stability of the solution in the capillary, with and without a chemically treated inner wall, were tested. Ferguson plots were used to assess the size selectivity of the separation.

Electrophoresis, Polyacrylamide Gel↗
PubMed1991

Capillary electrophoresis of DNA in agarose solutions at 40 degrees C.

DNA fragments ranging from 72 to 1353 bp in length (phi X174 RF DNA/HaeIII) were separated by capillary electrophoresis in 0.3-2.0% solutions of agarose (Sea-Plaque GTG) at 40 degrees C. Liquified agarose above its gelling temperature is easily filled and refilled into capillaries. Its background absorbance at 260 nm was sufficiently low to allow for DNA detection at an estimated DNA load of 13 ng/10 components. Sample injection proceeded at 1 kV for 16 s. The internal capillary diameter was 150 mu, the migration path 27 cm. Migration times varied from 5 to 14 min at 185 V/cm. Potentially, the applicability of capillary electrophoresis in agarose solutions can be expected to extend to the entire size range of DNA, in view of the recent demonstration of kb-sized circular DNA separations in agarose solutions, and those of Mb-sized DNA-agarose complexes in linear polyacrylamide solutions.

DNA↗
PubMed1990

Applicability of dynamic change of pH in the capillary zone electrophoresis of proteins.

A method to extend the separation power of CZE is described. The method is based on the separation of sample components at two different pH values during one separation run, and involves dynamic buffering of the pH inside a separation capillary by controlling the flow of H+ ions from the anodic electrode chamber. By changing the anolyte in the chamber, a dynamic pH step is generated, which proceeds rapidly along the capillary and establishes the required new pH value. The use of the method has been demonstrated by the cationic separation of a model mixture of proteins.

Animals↗
PubMed1990

Mathematical description of electrophoretic separation of weak acids by means of an H+ pulse.

The paper gives a detailed theoretical description of the recently published principle of separation by a dynamic pulse in zone electrophoresis. The theory is illustrated by using a system in which weak acids are separated by migrating against an H+ pulse. The mathematical description pertains to (i) the evolution and migration of the concentration profile of the H+ pulse, and (ii) the migration of a sample substance (here a weak acid) against and through the pulse. As a result the migration (detection) times of the separated sample components are obtained. Based on the theory, a graphical treatment was developed which allows fast optimization of the separation conditions by observing (on the PC monitor) how the trajectories of the substances (drawn in a time vs. distance coordinate system) change with a change in the parameters of the pulse. Some of the results illustrate the possible advantages of using the dynamic pulse method in analytical practice.

Acids↗
PubMed1990

Enantiomer resolution by using capillary zone electrophoresis: resolution of racemic tryptophan and determination of the enantiomer composition of commercial pharmaceutical epinephrine.

The enantiomers of D- and L-tryptophan were separated by capillary electrophoresis, using alpha-cyclodextrin as a chiral active component in the background electrolyte. The separation of (-) and (+) epinephrine was achieved by supplementing the background electrolyte with Heptakis (2,6-di-O-methyl-beta-cyclodextrin). As a practical application of the method, the quantitative analysis of (-) and (+) enantiomers in commercial pharmaceutical solutions of adrenaline is shown.

Cyclodextrins↗