We are introducing a computer implementation of the mathematical model of zone electrophoresis (CZE) described in Stedry, M., Jaros, M., Hruska, V., Gas, B., Electrophoresis 2004, 25, 3071-3079 program PeakMaster. The computer model calculates eigenmobilities, which are the eigenvalues of the matrix tied to the linearized continuity equations, and which are responsible for the presence of system eigenzones (system zones, system peaks). The model also calculates other parameters of the background electrolyte (BGE)-pH, conductivity, buffer capacity, ionic strength, etc., and parameters of the separated analytes--effective mobility, transfer ratio, molar conductivity detection response, and relative velocity slope. This allows the assessment of the indirect detection, conductivity detection and peak broadening (peak distortion) due to electromigration dispersion. The computer model requires the input of the BGE composition, the list of analytes to be separated, and the system instrumental configuration. The output parameters of the model are directly comparable with experiments; the model also simulates electropherograms in a user-friendly way. We demonstrate a successful application of PeakMaster for inspection of BGEs having no stationary injection zone.
Simul 5 Complex is a one-dimensional dynamic simulation software designed for electrophoresis, and it is based on a numerical solution of the governing equations, which include electromigration, diffusion and acid-base equilibria. A new mathematical model has been derived and implemented that extends the simulation capabilities of the program by complexation equilibria. The simulation can be set up with any number of constituents (analytes), which are complexed by one complex-forming agent (ligand). The complexation stoichiometry is 1:1, which is typical for systems containing cyclodextrins as the ligand. Both the analytes and the ligand can have multiple dissociation states. Simul 5 Complex with the complexation mode runs under Windows and can be freely downloaded from our web page http://natur.cuni.cz/gas. The article has two separate parts. Here, the mathematical model is derived and tested by simulating the published results obtained by several methods used for the determination of complexation equilibrium constants: affinity capillary electrophoresis, vacancy affinity capillary electrophoresis, Hummel-Dreyer method, vacancy peak method, frontal analysis, and frontal analysis continuous capillary electrophoresis. In the second part of the paper, the agreement of the simulated and the experimental data is shown and discussed.
The effective mobilities of the cationic forms of common amino acids--mostly proteinogenic--were determined by capillary zone electrophoresis in acidic background electrolytes at pH between 2.0 and 3.2. The underivatized amino acids were detected by the double contactless conductivity detector. Experimentally measured effective mobilities were fitted with the suitable regression functions in dependence on pH of the background electrolyte. The parameters of the given regression function corresponded to the values of the actual mobilities and the mixed dissociation constants (combining activities and concentrations) of the compound related to the actual ionic strength. McInnes approximation and Onsager theory were used to obtain thermodynamic dissociation constants (pK(a)) and limiting (absolute) ionic mobilities.
The effect of ionic strength of the background electrolyte (BGE) composed of tris(hydroxymethyl)aminomethane (Tris) and acetic acid on the electrophoretic mobility of mono-, di- and trivalent anions of aliphatic and aromatic carboxylic and sulfonic acids was investigated by capillary zone electrophoresis (CZE). Actual ionic mobilities of the above anions were determined from their CZE separations in Tris-acetate BGEs of pH 8.1 to 8.2 in the 3 to 100 mM ionic strength interval at constant temperature (25 degrees C). It was found that the ionic strength dependence of experimentally determined actual ionic mobilities does not follow the course supposed by the classical Onsager theory. A steeper decrease of actual ionic mobilities with the increasing ionic strength of BGE and a higher estimated limiting mobility of the anions than that found in the literature could be attributed to the specific behavior of the Tris-acetate BGEs. Presumably, not only a single type of interaction of anionic analytes with BGE constituents but rather the combination of effects, such as ion association or complexation equilibria, seems to be responsible for the observed deviation of the concentration dependence of the actual ionic mobilities from the Onsager theory. Additionally, several methods for the determination of limiting ionic mobilities from CZE measured actual ionic mobilities were evaluated. It turned out that the determined limiting ionic mobilities significantly depend on the calculation procedure used.
The stability (affinity, association, binding, complexation, formation) constant characterizes binding interaction between the analyte and the complexing agent. Knowledge of the stability constant makes possible the prediction and estimation of the binding behavior of constituents (amino acids, peptides, proteins, drugs, antibiotics, enzymes, enantiomers) to their partners, and the finding of a suitable partner for the given analyte to form a stable complex. The present paper summarizes the stability constant determination methods and the approaches used to evaluate the experimental data. Further, the paper recapitulates the published stability constant values determined, mainly, by capillary electrophoretic methods, taken from the Web of Science database covering the last decade. Details of the experimental conditions employed for the determination of the stability constants are also given. The review attempts to give a critical evaluation of the problems that accompany the determination of stability constant and discusses their solution.
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