Jiří Vacík

High-frequency contactless conductivity detection in isotachophoresis

Summary A new detection system for isotachophoresis, the high-frequency contactless conductivity detector, is described. This detector has a high resolving power and gives good reproducibility.

Computer-aided simulation of electromigration

Abstract Equations that describe the electrophoretic migration of monovalent ionic substances in solution with a significant presence of H + or OH − ions are formulated. A derivation of the Kohlrausch regulating function for these conditions is presented. The model of electromigration consists of a set of continuity equations, together with a set of algebraic equations describing the chemical equilibria involved, and is implemented on a personal computer. Simulation of some experimental phenomena in electrophoretic methods, e.g ., the sharpening effect in capillary zone electrophoresis or anomalous spikes in isotachophoretic systems, is presented.

Improvement of the performance of a high-frequency contactless conductivity detector for isotachophoresis

Abstract Modifications to a high-frequency contactless detector are described. Its properties (reproducibility, stability and dependence of the sensitivity on the concentration or conductivity and relative permittivity of the measured solutions) are demonstrated and its applicability to capillary isotachophoresis is illustrated on the example of a separation of a test mixture.

Capillary isotachophoresis with ultraviolet detection some quantitative aspects

Abstract Equations showing that the zone length (or detection time) measured is usually not directly but only linearly proportional to the amount of sample injected, are derived. The basic theory of UV detector response is presented, and the use of UV detector response as a quantitative measure for small amounts of UV absorbing compounds is demonstrated. Using this technique complete analysis of mixtures containing components differing in relative amounts by up to four orders of magnitude were performed in one experiment with no counterflow needed.

Simulated quantitative and qualitative isotachophoretic indices of 73 amino acids and peptides in the pH range 6.4–10

Qualitative and quantitative isotachophoretic indices of 73 amino acids, dipeptides and tripeptides were simulated under 24 leading electrolyte conditions covering the pH range 6.4-10. The RE values and time-based zone lengths are tabulated together with the absolute mobility (m0) and pKa values used. The leading electrolyte used was 10 mM HCl and the pH buffers were imidazole, tris(hydroxymethylamino)methane, 2-amino-2-methyl-1,3-propanediol and ethanolamine. The simulated indices will be useful in the assessment of the separability and determination of the listed and related compounds.

Isotachophoretic determination of anionic and cationic species in well and surface waters

Electrolyte systems and the conditions for the isotachophoretic determination of anions () and cations (K+, Na+, Cal2+, Mg2+) in well and surface waters are described. The results of isotachophoretic determinations on practical samples are compared with those obtained by classical methods.

Determination of dissociation constants of weak electrolytes by capillary isotachophoresis

Abstract The method described for the determination of the dissociation constants of weak electrolytes is based on the fact that the effective mobility of a weak electrolyte is a function of pH. Dissociation constants (together with actual mobilities of ionic forms of the given weak electrolyte) are parameters of this function. On the basis of a mathematical model of the isotachophoretic (ITP) steady state, a set of appropriate pairs of pHs and effective mobilities is calculated and dissociation constants are obtained from them by a non-linear least-squares procedure. The method was validated by calculation of the dissociation constants and absolute ionic conductivities of anions of weak organic acids (formic, acetic, propionic, oxalic, malonic, succinic, adipic and citric) from the data obtained by their ITP analysis using fourteen different electrolyte systems in the pH range 3.1–7.9. Good agreement with literature values was achieved.

Determination of limiting ionic mobilities and dissociation constants of some local anaesthtics

The limiting ionic mobilities and thermodynamic acid dissociation constants were calculated from isotachophoretic experiments for the local anaesthetics procaine, tetracaine, lidocaine, trimecaine, bupivacaine, cinchocaine, diperodone, diocaine, cocaine, psicaine-neu, tropacocaine, amylocaine, beta-eucaine and leucinocaine. The pH values at which the local anaesthetics with very similar limiting ionic mobilities can be isotachophoretically separated were determined from simulated mobility curves. The measuring apparatus employed a high-frequency contactless conductivity detector.

Dynamics of isotachophoretic separation : I. Computer simulation

Abstract A simulation model formulated on an EAI 690 hybrid computer system is described. This model makes it possible to simulate with very good precision the dynamics not only of isotachophoretic, but also of any electrophoretic separation of the maximum number of four strong, uni—univalent electrolytes with a common counter ion.

Capillary isotachophoresis with electrolyte counter-flow : Temperature and concentration profiles of the zone boundary

Abstract A conductivity sensor was constructed which can be incorporated into instruments for capillary isotachophoresis. The appropriate electronic equipment was developed using the perspective inland component base. A new method of proportional counter-flow regulation was designed which can be applied to any apparatus, irrespective of the detection method. It was shown that the temperature profile of the zone boundary can be sharpened by decreasing the boundary velocity by means of an appropriate counter-flow. The temperature and conductivity profiles of the zone boundary were characterized by means of second central moments. By this comparison it was shown unambiguously that conductivity detection is more advantageous. Comparison of thermometric and conductivity detections showed that the latter is more sensitive by more than two orders.