Jaroslav Janák

Use of complex formation equilibria in the analytical isotachophoresis of strong electrolyte ions : Separation of halides and sulphates

Abstract The possibility of effecting isotachophoretic separations by means of complex formation equilibria between a counter ion and the components being separated was investigated. This procedure was shown to be of potential significance mainly for the separation of ionic species of strong electrolytes, and the separation of sulphates and halides was examined. The use of Cd(II) as a counter ion and NO3− as a leading ion is suggested. The migration of sulphate and nitrate zones is considered theoretically, and data calculated for actual operating conditions are verified experimentally.

Instrumentation for high-speed isotachophoresis

Abstract The design and operating parameters of the individual elements of an isotachophoregraph were examined from the viewpoint of rapid quantitative analysis. An arrangement comprising an inlet port, separation column and detection cell was constructed, in which dead spaces were eliminated and the capillary and detection cell were efficiently cooled. This arrangement permits the time of isotachophoretic analysis from the instant of sample introduction to be shortened to 3-5 min, the development of the isotachophoregram proper taking 20-40 sec. The basis of the arrangement is a monolithic block of Perspex that comprises both electrode compartments, control stopcocks of the sampling device and the capillary. The latter is formed by a flat groove in the block, closed with a PTFE foil overlapping the groove and compressed on to the block with a thermostatted metallic plate. The detection cell is formed by part of the capillary and consists of two platinum contacts that extend into the groove in the monolithic block. The detector functions by sensing the electric gradient of the migrating zone. Recording was effected by means of a home-made voltmeter of high input resistance, with the detector input insulated electrically from the output of the recorder. The high-voltage source employed was also home made and yielded a stabilized current of up to 400 μA at 16 kV.

Statistische auswertung der messmethoden zur quantitativen bearbeitung von registrierten differentialkurven in der gas-chromatographie

Zusammenfassung In der Literatur und Praxis von heute verwendet man zur Messung der gas-chromatographischen Kurven verschiedene Methoden unter der Voraussetzung, dass sie mit einem Fehler von 1–3 % behaftet sind. Um Klarheit in diesen Zustand zu bringen, haben wir ungefahr 100 Analysen mit Hilfe von 7 konstruktieven und 3 automatischen Methoden statistisch verarbeitet. Die konstruktiven Methoden wurden gepruft: Planimetrieren; wiederholtes Planimetrieren; Wiegen des Papiers mit unter den Kurven ausgeschnittenen Flachen; Quadratur der Kurve mit Hilfe des Produktes der Hohe und der Breite in der halben Hohe und mit Hilfe der Uberlagerung eines Dreiecks durch Tangenten in den Inflexionspunkten der Kurve; Messung der Hohe der Kurve und Messung der Flache, Hohe mal Elutionszeit, bezw. mal Entfernung des Maximums vom Anfang des Chromatogramms. Von den automatischen Methoden wurden drei Haupttypen von Integratoren, und zwar ein mechanischer, ein elektromechanischer und ein rein elektronischer Integrator uberpruft. Der mechanische Integrator arbeitet auf dem Prinzip eines Systems von rotierendem Rad und Programm-Scheibendaumen. Der elektromechanische Typus ubertragt die Anderung der verstarkten Spannung vom Detektor des Chromatographen auf die Umdrehung eines Gleichstrom-Elektrometers; der elektronische Integrator war einer vom Analogtypus. Es wurden die mittleren Fehler fur verschiedene Flachengrossen (0–50 mm 2 , 51–100 mm 2 , 101–300 mm 2 und 301–1200 mm 2 ) festgestellt. Zusammenfassend kann gesagt werden, dass heutzutage gewohnlich noch nicht optimale Methoden verwendet werden.

High-speed isotachophoresis: current supply and detection system

Abstract A stabilized d.c. power supply for high-speed analytical isotachophoresis, providing a stepless constant current adjustable up to 400 μA at a voltage up to 16 kV, and a detection system for the direct measurement of potential gradients in isotachophoretic zones are described. The design enables any of the power supply output terminals to be earthed. Hence the detection cell can be kept at a relatively low above-earth potential when analyzing both anions and cations. It has been verified that the ionic species separated can be identified by determining the relative ratios of the potential gradients in their zones and by comparing these experimental data with the inverse values of the relative ratios of the tabulated mobilities. The relative deviations found did not exceed 2% for a model mixture of inorganic anions.

Multi-dimensional chromatography using different developing methods

Abstract A new multi-dimensional chromatographic technique is described, μg to mg quantities from the gas chromatogram are placed on the start-line of a thin layer of adsorbent or of a sheet of chromatographic paper, which is moved past the orifice of the gas chromatograph and then developed in the usual manner. Thus, separation of the materials is obtained by exploiting the two most extreme possibilities given by the existing chromatographic methods, viz. gas—liquid chromatography, which separates according to the relative volatility of compounds (in the direction of the time-axis along the start), and thin-layer chromatography or paper chromatography, which separate according to the type of the functional group (in the vertical direction). After the extraction of the separated materials from the thin-layer or paper, GLC, on a suitably selected stationary phase, may be repeated if necessary. The theor for separation and experimental details are given. Further possibilities are obtainable by programming the driving velocity of the plate (paper) which acts in the same manner as temperature programming of a GC column. The method described was used successfully in the research on the composition of coal tar, but can be applied to other complex mixtures of compounds of different chemical character.

Analytical isotachophoresis : The concept of the separation capacity

Abstract The concept of separation capacity in isotachophoresis has been investigated in order that the analytical separation possibilities may be predicted for given working conditions. A relationship has been derived between the amount and composition of a binary mixture under isotachophoretic separation and the amount of electricity which has to be passed through the system to obtain complete separation of the mixture. By using this relationship, values of the separation capacity have been calculated for three two-component mixtures analyzed by means of two isotachophoretic instruments and verified experimentally.

Gas chromatography of all C15C18 linear alkenes on capillary columns with very high resolution power

Abstract Conditions were studied for the separation of mixtures of all the 60 isomers of C 15 C 18 n -alkenes in the presence of the corresponding n -alkanes in highly efficient glass capillary columns ( N ≈ 0.5·10 6 effective plates for n -alkenes with k ≈ 3), coated with C 87 hydrocarbon, Apiezon L or Carbowax 20M as stationary phase. The separation of cis - and trans -isomers of n -alkenes is made possible at a sufficiently high column efficiency by the different dependences of their retentions on temperature. The separation of positional isomers of n -alkenes having even carbon numbers for the pairs with the most centrally situated double bonds can be achieved only by use of highly efficient columns with polar or non-polar stationary phases ( n req ≈ 10 6 plates). Correlations between the structure and increments H , δ I , d I /d T and Δ I , derived from retention indices of n -alkenes, were used for identification as they reflect the position of the double bond, the geometrical arrangement and the length of the carbon chain in various isomers. The so-called propyl effect was confirmed for trans -4-alkenes, disturbing the regularity of all correlations between structure and retention. The influence of adsorption of n -alkanes and n -alkenes at the polar phase-carrier gas interface on the retention characteristics is discussed. Reproducibility of retention indices of n -alkene isomers is a function of their capacity ratios (thickness of the stationary phase film in the column), decreases with polarity of the stationary phase and the isomer under analysis and with the difference between a reference standard and the n -alken ein question. These effects are so significant for the columns with Carbowax 20M that a different retention sequence was found for some n -alkene isomers in columns with relatively small differences in the thickness of the stationary phase.

Capillary gas chromatography of alkylbenzenes : II. Correlations between the structures and methylene group increments and differences in retention indices of isomers

Abstract The contribution to gas chromatographic retention behaviour of methylene group increments and differences in the retention indices (δ I ) of isomers of alkylbenzenes up to C 16 on squalane and acetyltri- n -butyl citrate was studied. The methylene group increments appear to vary over a wide range (60–100 i.u.) and depend on the magnitude, positions and relative lengths of the alkyl chains and on the number of carbon atoms. Anomalous retention behaviour of n -propylbenzene and its derivatives, except for molecules in which there are alkyl groups in both positions vicinal to the n -propyl group, was found. Hence, the correlations of I CH 2 in homologous series can serve as indicators of fine structural peculiarities of the molecules. The applicability of regularities in methylene group increments and δ I values, based on precise measurements of retention indices of low-molecular-weight alkylbenzenes, for confirmation of the identities of high-molecular-weight alkylbenzenes ( > C 10 ) is demonstrated.

Isotachophoresis of Kinetically labile complexes

Abstract This paper deals both theoretically and experimentally withe the behaviour of kinetically labile anionic complexes under the conditions of isotachophoretic migration. It has been shown that in an isotachophoretic zone of an anio nic metal—ligand complex, owing to the dissociation equilibrium free metal cations and free ligand anions are present, which, in proportion to the signs and values of their mobilities, migrate out of the zone of the complex. The migrating zone of the complex, leaving behind a trace of the free metal cation, appears as a bleeding zone and decomposes slowly in the course of the migration. A mathematical description of the decomposing zone is elaborated, giving the decomposition rate of the complex depending on the conditional complex stability constant, operational parameters of the column and the composition of the leading electrolyte. It has been demonstrated that in both main cases of mutual movement of the complex and the free ligand (the ligand overtakes the complex or lags behind it) the decomposition of the complex during the migration can be negligible under properly selected operating conditions (mainly the composition of the leading electrolyte), and the zone will appear isotachophoretically stable and can be utilized for quantitative analysis. Model experiments with NTA and EDTA complexes agree with the theory. The model described makes it possible both to predict the isotachophoretic behaviour of anionic complexes under the given operating conditions and to select these conditions so that the stability of the zones of the complexes under investigation may be influenced selectivity in order to obtain the required separation.

Separation of some typical krebs cycle acids by high-speed isotachophoresis

In order to perform a required separation, an experimental procedure for the selection of suitable operating conditions is suggested and discussed. It is based on measurements of the dependences of the relative effective mobilities of the components under investigation on the pH of the leading electrolyte. The procedure was applied to a set of typical Krebs cycle acids and the values of the relative effective mobilities measured are given in tables and graphs. A pH of 3.8 was selected as the most suitable. At this value, the acids investigated were successfully separated in less than 4 min using 0.011 M hydrochloric acid + beta-alanine as the leading electrolyte.