Biomedical subjects

Petr Gebauer

Publications and source records attributed to Petr Gebauer.

14 recordsLinked to original sources

PubMed2007

Recent progress in capillary ITP.

ITP has been attracting constant attention for many years due to its principal capability to concentrate trace analytes by several orders of magnitude. In the current capillary format, it is able to concentrate trace analytes diluted to several microliters of an original sample into concentrated zones having volumes in the range of picoliters. Due to this reason, ITP holds an important position in many current multistage and multidimensional separation schemes. This article links up previous reviews on the topic and summarizes the progress of analytical capillary ITP since 2002. Almost 100 papers are reviewed that include methodological novelties, instrumental aspects, and analytical applications. Papers using ITP and/or isotachophoretic principles as part of multistage and/or multidimensional separation schemes are also included.

Chemistry, Pharmaceutical↗

PubMed2007

Contemporary sample stacking in CE: a sophisticated tool based on simple principles.

Sample stacking is a general term for methods in CE which are used for on-line concentration of diluted analytes. During the stacking process, analytes present at low concentrations in a long injected sample zone are concentrated into a short zone (stack). The stacked analytes are then separated and individual zones are detected. Thus stacking provides better separation efficiency and detection sensitivity. Many papers have been published on stacking till now, various procedures have been described, and, many names have been proposed for stacking procedures utilizing the same principles. This contribution brings an easy and unified view on stacking, describes the basic principles utilized, makes a list of recognized operational principles and brings an overview of principal current procedures. Further, it surveys selected recent practical applications ordered according to their operational principles and includes the terms, nicknames, and acronyms used for these actual stacking procedures. This contribution may help both newcomers and experts in the field of CE to orient themselves in the already quite complex topic of sample stacking.

Electrophoresis, Capillary↗

PubMed2006

A new type of migrating zone boundary in electrophoresis: 2. Transient sample zone shapes.

A new type of migrating zone boundary in electrophoresis is presented theoretically and evidenced experimentally. This type of the boundary (called hybrid boundary) shows simultaneously a steady-state part with self-sharpening properties and an unsteady-state part with time-dependent electromigration dispersion. It is shown that a sample zone may possess a hybrid boundary both as its front and rear one simultaneously. In such a case, the evolution of a sample zone injected originally as a rectangular pulse exhibits very complex transient shapes before it reaches the well-known fronting or tailing triangular shape. Depending on the stage at which detection of such a sample zone occurs, variable and peculiar-shape peaks may appear in the electropherogram. Based on theoretical predictions, experimental examples of the above-mentioned phenomena are presented in this contribution for direct and indirect UV absorbance detection of sample zones. Excellent agreement of theoretical predictions with the experiments has been found. The knowledge of hybrid boundaries is of key significance for correct interpretation of records of CE analyses in practice.

Electrophoresis↗

PubMed2006

A new type of migrating zone boundary in electrophoresis: 3. The hybrid boundary and stacking criteria.

This article investigates the principles of stacking of analytes by a zone of a bulk sample component that possesses one hybrid boundary. The model system investigated comprises a transient stacking zone in a BGE where the rear boundary of this zone is a hybrid one. A theoretical description of such a system is given, and general rules and mathematical criteria for quantitative stacking are presented. These criteria are based on comparison of migration velocities of analytes to be stacked and velocities of the boundaries of the stacking zone. It is shown that the presence of a hybrid boundary brings about additional constraints for stacking of analytes due to the presence of the sharp part of the hybrid boundary that migrates faster than regular sharp boundary of this zone. An experimental example related to the described theory is also shown.

Computer Simulation↗

PubMed2006

Properties of moving boundaries in electrophoretic systems with multivalent weak electrolytes: principles of non-Kohlrausch concentration adjustment.

This paper describes the properties of electrophoretic moving boundaries in systems containing multivalent weak electrolytes where the Kohlrausch regulating law is not valid. It is shown that zones of unexpected properties can be formed in such systems and that the adjusted concentrations in these zones cannot be predicted using present knowledge. A theoretical approach to the properties of such "non-Kohlrausch" systems is presented that allows the explanation and prediction of their properties. The theory based on velocity diagrams describes the electrophoretic evolution of a concentration boundary between a pair of zones (differing only in the concentration ratio of their components) as the formation of two moving boundaries migrating in opposite directions. The concentration profiles and velocities of these moving boundaries, that can be either sharp or broadening by electromigration dispersion, as well as the adjusted concentrations in the formed intermediate zones can be predicted from calculated velocity diagrams. Such zones differ from normal systems in that their adjusted concentrations are a function of the composition of both zones that formed the original boundary. The theory is illustrated and verified by both computer simulations and experiments.

Computer Simulation↗

PubMed2006

Determination of trace cationic impurities in butylmethylimidazolium-based ionic liquids: from transient to comprehensive single-capillary counterflow isotachophoresis-zone electrophoresis.

Determination of impurities in ionic liquids (ILs) remains a difficult task. In this work, the hyphenation of isotachophoretic (ITP) preconcentration to zone electrophoresis (ZE) has been explored for the trace analysis of the cationic impurities Na(+), Li(+), and methylimidazolium (MI(+)) in butylmethylimidazolium (BMI(+))-based ILs. Simultaneous detection of UV-transparent and UV-absorbing impurities was ensured by a BGE composed of creatinine-acetate buffer. To induce ITP, three different strategies were evaluated: (i) Sample self-stacking ensured by the addition of ammonium acetate (NH(4)Ac) to 25-50-fold diluted IL solution (transient ITP). (ii) Complete ITP-ZE separation performed in a single capillary: ITP was realized in discontinuous electrolytes comprising an 80 mM NH(4)Ac, 40 mM acetic acid, 30 mM alpha-CD, pH 5.05, leading electrolyte (LE) and a 10 mM creatinine, 10 mM acetic acid, pH 4.9, terminating electrolyte (TE). To create the ZE stage, the ITP stack of analytes was moved back toward the capillary inlet by pressure and simultaneously the capillary was filled with the BGE. This protocol made it possible to accommodate a 2.5-times diluted IL sample. (iii) Complete counterflow ITP-ZE with continuous electrokinetic sample supply: the ITP stage was performed in a capillary filled with a 150 mM NH(4)Ac, 75 mM acetic acid, 30 mM alpha-CD, pH 5.0 LE, with 40-times diluted IL at the capillary inlet. BMI(+) from IL acts as the terminating ion. The LODs reached in this latter case were at the 10 and 1 ppb levels for MI(+) and Li(+) in diluted IL matrix, respectively.

Buffers↗

PubMed2005

A new type of migrating zone boundary in electrophoresis: 1. General description of boundary behavior based on electromigration dispersion velocity profiles.

Till now two principal types of electrophoretic boundaries have been recognized: a steady-state one showing self-sharpening properties and an unsteady-state one showing electromigration dispersion (EMD). In this contribution, the existence of a third (hybrid) type of electrophoretic boundary is revealed, that shows simultaneously: (i) steady-state character with self-sharpening properties in a certain part of the boundary, demarcated by a certain range of its composition; (ii) unsteady-state character with EMD in the resting part. A new theoretical approach to the study of the structure and properties of electrophoretic boundaries is presented, based on EMD velocity profiles representing the dependence of the EMD velocity on the composition in any point of the transition region across the boundary. According to this approach, the linearity or nonlinearity of the EMD velocity profile is recommended as the criterion for distinguishing the actual type of the boundary in question. It is shown that the new type of electrophoretic boundary is not an exotic case but may be observed even in simple systems as, e.g., formed by adjacent zones containing mixtures of current species such as picrate and acetate. Computer simulations are presented which confirm the theoretical conclusions and illustrate the three types of electrophoretic boundaries.

Electrophoresis, Capillary↗

PubMed2004

Ionic boundaries in biological capillary electrophoresis.

Ion migration in electrophoresis always leads to the formation of ionic boundaries. While some types of the ionic boundaries can be formed intentionally, e.g., to improve separation efficiency or sensitivity of the analysis, other, naturally formed boundaries, may cause unexpected effects during the electrophoretic experiment. Some of the boundaries often go unnoticed in practice; however, many effects of the ionic boundaries formed by the sample matrix and background electrolyte components are frequently observed in capillary electrophoresis (CE). The interpretation of these effects may not be trivial and different explanations of the same phenomena may be found in the literature. This critical article attempts to review some of the important effects of the ionic boundaries observed or utilized during the CE of biologically important samples.

Electrophoresis, Capillary↗

PubMed2004

Experimental assessment of electromigration properties of background electrolytes in capillary zone electrophoresis.

Electromigration dispersion (EMD) properties of background electrolytes (BGEs) used in capillary zone electrophoresis (CZE) are of key importance for the success of an analysis. The knowledge of these properties may serve well for the prediction of the asymmetry of peaks of analytes, for the prediction of unsafe regions where a strong interference of system zones may be expected, and for the selection of optimum conditions where the analytes of interest may give sharp and practically symmetric peaks. Present theories enable one to calculate and predict EMD properties of many BGEs but there is also a lot of BGEs that are beyond the present theoretical models as far as their composition and equilibria involved are considered. This contribution brings a method for assessment of EMD properties of any BGE from easily accessible experimental data. The method proposed is illustrated by model examples both for cationic and anionic separations. Imidazole acetate, histamine acetate, and histidine acetate served as model BGEs for cationic separations; as the model BGE for anionic separations, Tris-borate and sodium-borate BGEs have been selected since these buffers are frequently used and borate is well-known for its complexing equilibria in aqueous solutions.

Acetates↗

PubMed2004

Importance of the counterion in optimization of a borate electrolyte system for analyses of anions in samples with complex matrices performed by capillary zone electrophoresis.

Borate buffers are common background electrolytes for analyses of anions in capillary zone electrophoresis. Usually, sodium borate at a given pH is used and this specification seems to be sufficient for a successful analysis. In this paper, we show that free migration of OH(-) may deteriorate the analysis of a typical anionic analysis of clinical samples due to uncontrolled migration of OH(-) throughout the systems of analyzed zones and may damage the stacking of anionic analytes of interest. We have proven that the use of ammonium borate may remedy the situation where the presence of ammonium may selectively stop the free migration of OH(-) ions, slow down their effective mobility and bring their safe behavior resulting in reproducible stacking of clinically important anions. Results of real analyses of human serum samples confirmed the proposed method and proved that substitution of sodium for ammonium in borate buffers offers reliable analyses of clinical samples having chloride as the bulk component. The experimental results given in this paper are supported also by computer simulation, which can not only support the positive results but also show the dynamics of the separation that is otherwise hidden to any detection possibilities.

Borates↗

PubMed2003

Chloride present in biological samples as a tool for enhancement of sensitivity in capillary zone electrophoretic analysis of anionic trace analytes.

Effects originating from the variability of the sample matrix can be efficiently eliminated when the separation conditions are selected so that compounds of like charge with high concentration referred to as macrocomponents are embodied into the system of transient isotachophoresis. For stacking and separation of anionic trace analytes in biological samples, the presence of chloride is shown to be important to balance out effects of other macrocomponents that act against isotachophoretic stacking. Having acetoacetate, malate, citrate, and some drug metabolites in untreated human serum samples, the stacking mechanism of these compounds in an electrolyte system comprising 5 mM mandelic acid and epsilon -aminocaproic acid, pH 3.8, is explained. Analytes are monitored by indirect UV-absorption detection. Attention is paid to the minimum chloride concentration required with respect to the concentration ratio of phosphate (stacker) and lactate (destacker) present in the sample so as to ensure both stacking and separation of trace analytes. Insight into the separation process is given both with computer simulations and experiments. For selected analytes, the effect of chloride concentration on quantitative evaluation, sensitivity and limit of detection is demonstrated as well. Moreover, the applicability of the mobility window between phosphate and lactate for an additional group of metabolites is sketched.

Anions↗

PubMed2002

Theory of system zones in capillary zone electrophoresis.

In the last years, it has been shown that the formation and migration of system zones is an inherent feature of capillary zone electrophoresis (CZE) and that it depends predominantly on the composition of an actual background electrolyte (BGE). In most of the currently used BGEs, the SZs are invisible by the UV absorbance detection system, however, the comigration of SZs with the zones of analytes deteriorates the analytical performance of CZE and may be fatal for its utilization. Therefore, the theoretical predictions of the existence and migration of SZs is of key importance for the expediency of CZE. This is a review of the theoretical treatments of SZs which reveals the origin and the properties of SZs and shows how to cope with them. Also, a table of some typical BGEs is presented where the existence and mobilities of SZs are given.

Electrophoresis, Capillary↗

PubMed2002

Quantitation of trace analytes in capillary zone electrophoresis with UV-absorbance detection: a critical study of approaches based on peak height.

This contribution is aimed at providing a survey of the limitations of the peak-height technique. It is shown that the shape and the slope of calibration curves give a precise insight into the separation mechanism and can warn the analyst against improper selection of background electrolyte or sample dilution. This work investigates three typical situations where the sample contains (i) the minor analyte only, (ii) the minor analyte and a nonstacking bulk component, (iii) the minor analyte and a stacking bulk component, and various modes of measurement of the calibration curves differing in the medium used for the dilution of the original sample (water, background electrolyte, solution of the bulk component). Based on simple theoretical models, the shapes of the calibration curves are derived and elucidated for all modes, clearly demonstrating that only a few modes can provide useful results while most of them seem useless for quantitation. The knowledge of regularities affecting the character of calibration curves can be used for optimization of the analysis so that reliable results and highest attainable sensitivity can be reached. The outcome of this study brings a clear instruction how to successfully quantitate trace analytes even in samples with a complex and variable matrix*.

Electrolytes↗

PubMed2002

Recent progress in capillary isotachophoresis.

This article is a continuation of previous reviews and summarizes the progress of analytical capillary isotachophoresis since 2000. Papers reviewed include methodological and instrumental aspects as well as analytical applications. Included are also papers using isotachophoresis and/or isotachophoretic principles as part of multidimensional separation schemes.

Electrophoresis, Capillary↗