Biomedical subjects

Petr Bocek

Publications and source records attributed to Petr Bocek.

10 recordsLinked to original sources

PubMed2003

Capillary zone electrophoresis in methanol: migration behavior and background electrolytes.

Nonaqueous (NA) solutions are often used as background electrolytes (BGEs) and NA solvents are added to aqueous BGEs as organic modifiers in capillary zone electrophoresis (CZE), in order to optimize the separations. This can be tricky, however, because the pH* and pK* concepts may be totally different in NA solvents, whereas often less knowledge is available concerning phenomena, such as system zones, applying NA solvents. In this paper, the concepts of pH* and pK* are considered for methanol as a solvent and pK* values are determined for several components in mixtures of water and methanol. With a mathematical model, adapted for calculations in methanol, parameters are calculated describing the fronting or tailing character of peaks and the question of peaks or dips, and the existence of system zones is discussed for pure methanol as a solvent. These aspects are experimentally verified, applying BGEs useful for the separation of cationic species in the indirect UV mode. It can be concluded that the mathematical model developed for aqueous BGEs is applicable to BGEs in methanol, too, and that the behavior of BGEs in methanol is comparable with that in water concerning the fronting or tailing character of peaks and the question of peaks and dips, although the mobilities and pK values can change significantly.

Electrolytes↗

PubMed2003

Stacking phenomena in electromigration: From basic principles to practical procedures.

The review describes principles of procedures and techniques used in capillary zone electrophoresis for enhancement of sensitivity that are based on increasing analyte mass in its zone during the electromigration process, for which the term stacking is generally used. Attention is paid to intrinsic stacking in samples with low conductivity, transient isotachophoretic stacking applied in samples with high conductivity, and sweeping in micellar electrokinetic chromatography. Principles of these stacking schemes are explained, new procedures and instrumental arrangements are discussed, and all contributions involving stacking principles that have been published since the year 2000 are surveyed.

Chromatography, Micellar Electrokinetic Capillary↗

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↗

PubMed2003

The preparation of background electrolytes in capillary zone electrophoresis: golden rules and pitfalls.

In this article the methodology of the design of suitable background electrolytes (BGEs) in capillary zone electrophoresis (CZE) is described. The principal aspects of the role of a BGE in CZE are discussed with respect to an appropiate migration behavior of analytes, including the transport of the electric current, the buffering of pH, the Joule heat, the electro-endosmotic flow (EOF) and the principal migration and detection modes. The impact of the composition of the BGE upon migration and detection is discussed. It is shown that the total concentration of the BGE is a principal factor and the adjustment of migrating analyte zones according to the Kohlrausch regulating function (KRF) is the principal effect in most of the sample stacking techniques. The number of co-ions and their properties are of key importance for peak shapes of the analyte peaks and for the existence of system zones. The detection of UV-transparent analytes may advanteously be done in the indirect UV mode, by using UV-absorbing co-ions, however, both peaks and dips may be expected in the UV trace in case of multiple co-ionic BGEs. Properties of BGEs can be predicted applying mathematical models and it is shown that with SystCharts, predictions can be given concerning the existence of system zones, detection modes and the peak shapes of analytes for a given BGE. Practical examples of methodological considerations are given in the design of suitable BGEs for four principal combinations of migration and detection modes. The properties of the BGEs selected are exemplified with experimental results. Golden rules are summarized for the preparation of suitable BGEs in CZE.

Electrolytes↗

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

Multivalent weak electrolytes - risky background electrolytes for capillary zone electrophoresis.

Multivalent weak acids and bases are useful components of buffers in electrophoresis. The use of such buffers as background electrolytes (BGEs) in capillary zone electrophoresis (CZE) is, however, risky due to the existence of unsafe regions in the analytical window of the separation. This contribution discusses the problems and shows that multivalent weak species in BGEs bring about the same effects as mixtures of two independent co-ions, i.e., the presence of two centers of symmetry in the electropherograms and the existence of a migrating system zone with a mobility in between these two centers of symmetry. The system zone deteriorates the analytical separation and detection of the analytes in its neighborhood. Illustrative experimental examples for both cationic and anionic CZE are shown and related discussion is given. Finally, some basic rules are formulated to avoid the preparation of risky BGEs.

Acids↗

PubMed2002

Multiple effect of surfactants used as additives in background electrolytes in capillary zone electrophoresis: cetyltrimethylammonium bromide as example of model surfactant.

Surfactants are frequently used in the preparation of background electrolytes (BGEs) in capillary zone elcetrophoresis (CZE) in order to affect and to optimize both the electroosmotic flow (EOF) and the separation process. Their effects are, however, always multiple, the resulting situation may be very complex and the separation process may even be destroyed. We use the surfactant cetyltrimethylammonium bromide (CTAB) as a model example and bring experimental results and related discussion which elucidate the multiple effect of surfactants in an integrated way. It is shown that even at concentration levels lower than 10(-4) M CTAB strongly reduces the cathodic EOF in bare fused-silica capillaries and converts it into anodic EOF. The magnitude and polarity of the EOF depends not only on the concentration of CTAB but also on the composition of BGEs used. The interactions of CTA cations with the bare capillary wall reduce sorption of cationic analytes and enables their analysis. CTA cations at levels below their critical micelles concentration (CMC) already interact with anionic analytes and reduce their mobilities. This association is strong with highly charged anions and by this, the reversal of the EOF, applying BGEs with highly charged anions is less effective. These interactions are competitive and also depend on the composition of the BGE used. At levels above its CMC, CTAB forms micelles and enables the application of the micellar electrokinetic capillary chromatography (MEKC) mode and the analysis of, e.g., neutral components. Simultaneously, it is shown that the presence of CTAB may increase the number of potentially formed system zones.

Cetrimonium↗

PubMed2002

Fast choice of separation conditions for analyses by capillary zone electrophoresis using an information system Xemic.

An information system Xemic applicable in analytical chemistry is described and its use in capillary electrophoresis for searching suitable separation conditions is demonstrated. This system is capable to provide suitable separation conditions even for analytes for which no electrophoretic experiments have been published so far. The system works with a database of components of anionic character the analyses of which have been performed, published in reviewed scientific journals, and included into a database created by an expert. Moreover, the system learned to search also in abstracts or complete scientific articles to find articles dealing with the determination of a substance in a given sample matrix. When no experiments have been published so far for a defined substance in a specific matrix, Xemic shows the separation conditions for determination of the substance regardless of the matrix. When no response can be found for the analyte of interest at all, the system Xemic works like an expert in the field and searches chemically similar substances and offers a series of substances the physicochemical properties of which are close to the followed analyte with respect to the behavior in the electric field, and shows working conditions for their analysis. Thus, the analyst puts only the order in the form of a given analyte in a given matrix and obtains a recommendation of a separation system that should enable to perform a successful separation. The system is not rigid and enables the operator to change the importance of individual attributes used in similarity search so as to obtain a broader or narrower group of similar components. With a certain probability the analyte of interest can be successfully analyzed under separation conditions that suited for the analysis of the most similar substances in the given matrix.

Computers↗

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↗