Michal Jaroš

Optimization of background electrolytes for capillary electrophoresis I. Mathematical and computational model.

A mathematical and computational model is introduced for optimization of background electrolyte systems for capillary zone electrophoresis of anions. The model takes into account mono- or di- or trivalent ions and allows also for modeling of highly acidic or alkaline electrolytes, where a presence of hydrogen and hydroxide ions is significant. At maximum, the electrolyte can contain two co-anions and two counter-cations. The mathematical relations of the model are formulated to enable an easy algorithmization and programming in a computer language. The model assesses the composition of the background electrolyte in the analyte zone, which enables prediction of the parameters of the system that are experimentally available, like the transfer ratio, which is a measure of the sensitivity in the indirect photometric detection or the molar conductivity detection response, which expresses the sensitivity of the conductivity detection. Furthermore, the model also enables the evaluation of a tendency of the analyte to undergo electromigration dispersion and allows the optimization of the composition of the background electrolyte to reach a good sensitivity of detection while still having the dispersion properties in the acceptable range. Although the model presented is aimed towards the separation of anions, it can be straightforwardly rearranged to serve for simulation of electromigration of cationic analytes. The suitability of the model is checked by inspecting the behavior of a phosphate buffer for analysis of anions. It is shown that parameters of the phosphate buffer when used at neutral and alkaline pH values possess singularities that indicate a possible occurrence of system peaks. Moreover, if the mobility of any analyte of the sample is close to the mobilities of the system peaks, the indirect detector signals following the background electrolyte properties will be heavily amplified and distorted. When a specific detector sensitive on presence of the analyte were used, the signal would be almost lost due to the excessive dispersion of the peak.

Optimization of background electrolytes for capillary electrophoresis: II. Computer simulation and comparison with experiments.

A mathematical and computational model described in the previous paper (Gaš, B., Coufal, P., Jaroš, M., Muzikář, J., Jelínek, L., J. Chromatogr. A 2001, 905, 269–279) is adapted, algorithmized, and a computer program PeakMaster having a status of freeware (http://natur.cuni.cz/∼gas) is introduced. The model enables optimization of background electrolyte (BGE) systems for capillary zone electrophoresis. The model allows putting to use uni‐ or di‐ or trivalent electrolytes and allows also for modeling highly acidic or alkaline BGEs. It takes into account the dependence of ionic mobilities and dissociation of weak electrolytes on the ionic strength. The model calculates the effective mobility of analytes and predicts parameters of the system that are experimentally available, such as the transfer ratio, which is a measure of the sensitivity in the indirect UV detection or the molar conductivity detection response, which expresses the sensitivity of the conductivity detection. Further, the model enables evaluation of a tendency of the analyte to undergo electromigration dispersion or peak broadening. The suitability of the model is verified by comparison of the predicted results with experiments, even under conditions that are far from ideal (under extreme pH and a high ionic strength).

New configuration in capillary isotachophoresis-capillary zone electrophoresis coupling.

The paper surveys possible configurations of a coupling capillary column operating in various electromigration modes. Special attention is given to capillary isotachophoresis-capillary zone electrophoresis (cITP-CZE) coupling and its description from the theoretical point of view. Computer simulations of separation are presented and compared with experiments. Further, we propose a new configuration of electrolyte systems in cITP-CZE coupling, which offers a possibility to perform complex analyses of micro- and macro-constituents in one run. The electrolyte system is verified by practical experiments for both anionic and cationic modes of analysis. The advantages and disadvantages of the new combination are discussed.