Physico-chemical applications of liquid chromatography I. Investigation of the adsorption of cardiac glycosides from water-ethanol solutions on silanized silica

Summary Using the cardiac glycoside cymarin as the example the application of liquid chromatography for the study of adsorption from solutions and the determination of the corresponding thermodynamic characteristics was investigated. The adsorption isotherm of cymarin at small concentrations from a water-ethanol solvent on silica gel modified by dimethyldichlorosilane was measured under static conditions using analytical LC to determine the concentrations of solutions after adsorption. The values of the Henry constants were obtained by extrapolating the slope of the adsorption isotherm down to zero concentration. The specific retention volumes for different but small sample sizes of cymarin in the chromatographic column were measured, the adsorbent and the water-ethanol eluent being the same as in the static conditions. The specific retention volume for a small (zero) sample size determined by liquid chromatography experiment coincides with the Henry constant of cymarin adsorption determined in static conditions. In favourable cases liquid chromatography can be used to determine the equilibrium constants for adsorption from solution. The dependence of the Henry constants on temperature was investigated for several cardiac glycosides. The influence of the modification of the adsorbent surface on the separation of the cardiac glycosides was also studied.     

Molecular interactions in adsorption liquid chromatography with mixed mobile phase

Summary The equation of Jaroniec was used to describe the molecular interactions in liquid adsorption chromatography with mixed mobile phases. The main object of the investigation was to demonstrate that the type of association in the bulk phase is independent of the nature of the stationary phase, and to examine the influence of the nature and number of components in the mobile phase upon the specific interactions in the system. The relationship between the type of association and the structure of the chromatographed substance was also taken into account.     

Influence of intermolecular interaction with the eluent on the retention of phenol and aniline on polar and non-polar surfaces

Summary The retention order of aniline and phenol on hydroxylated silica gel surface is reversed with the increase of the concentration of a polar component in the eluent. At minor (about 1%) concentrations of isopropanol in hexane aniline emerges first followed by phenol, the elution order being reversed with the increase of isopropanol concentration above 2%. The same behaviour is observed for silica gel with chemically bonded C₁₆ n-alkyl groups and for porous styrene-divinylbenzene copolymer. In all these cases the retention depends to a great extent on substance-eluent intermolecular interactions. At high isopropanol concentration in hexane the rise of column temperature changes the retention order of aniline and phenol on silica gel with hydroxylated surface since the association of these molecules with isopropanol as well as the isopropanol adsorption weaken as the temperature increases.     

Study of adsorption from solutions by frontal chromatography

Summary The automatic frontal chromatography installation was described. By this chromatographic method the adsorption isotherm of benzene from n-heptane solutions on hydroxylated surface of silica with various porosity has been determined. This investigation was performed at different flow rates of eluent and in a wide range of concentrations. The isotherm of adsorption obtained by this chromatographic method has been compared with the results of the static measurements. The coincidence of adsorption isotherms measured at the various flow rates are shown to be a criterion of proximity the chromatographic process to the equilibrium.     

A linear relationship between partition ratio and composition of a binary mobile phase in reversed-phase liquid chromatography using chemically bonded stationary phases

A simple linear relationship which enables the effect of the composition of a binary mobile phase on the retention of a solute to be assessed in reverse phase liquid chromatography using a bonded stationary phase has been derived. The equations have been tested using published experimental data.     

Reduction of silanophilic interactions in liquid chromatography with the use of ionic liquids

A suppression of silanophilic interactions by the selected ionic liquids added to the mobile phase in thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) is reported. Acetonitrile was used as the eluent, alone or with various concentrations of water and phosphoric buffer pH 3. Selectivity of the normal (NP) and the reversed (RP) stationary phase material was examined using a series of proton-acceptor basic drugs analytes. The ionic liquids studied appeared to significantly affect analyte retention in NP-TLC, RP-TLC and RP-HPLC systems tested. Consequently, the increased separation selectivity was attained. Due to ionic liquid additives to eluent even analytes could be chromatographed, which were not eluted from the silica-based stationary phase materials with 100% of acetonitrile in the mobile phase. Addition of ionic liquid already in very small concentration (0.5%, v/v) could reduce the amount of acetonitrile used during the optimization of basic analytes separations in TLC and HPLC systems. Moreover, the influence of temperature on the separation of basic analytes was demonstrated and considered in practical HPLC method development.     

Investigation of interactions between chloroderivatives of alkanes and alkenes and chemically bonded transition metal complexes by gas chromatography

Summary Interactions of Cu(II) complexes chemically bonded to the surface of silica with chloro-derivatives of alkanes and alkenes were investigated. It was found that chlorine as a substituent exerts a considerable influence on the retention of the individual chloro-derivatives. In the case of chloroalkenes this influence is negative while in the case of chloroalkanes it is positive. The magnitude of the observed effect depends on the number of substituents and on the way of their distribution within the molecule. Part III of a series on transition metal complexes in GC. Part II see ref. [1].     

A data base for polymer chromatography: Temperature dependence of interaction parameters in liquid adsorption chromatography

The temperature dependence of retention behaviour of polyethylene glycol (PEG) and its mono‐ and dimethyl ethers was studied on various RP columns in different mobile phases. The accessible volumes and the interaction parameters were determined from slope and intercept in a plot of the elution volumes of the oligomers of a polymer homologous series as a function of the difference of the elution volumes of consecutive oligomers. A quite different dependence of the interaction parameters was observed in the different mobile phases. While in methanol–water the interaction parameter decreases with increasing temperature, the opposite effect is observed in acetonitrile (ACN)–water. In acetone–water, the temperature dependence is almost negligible.     

Thin-layer adsorption chromatography with mixed mobile phases. 4. Extension of Ościk's equation to heterogeneous adsorbents

In this paper the equation for thin-layer adsorption chromatography with multicomponent mobile phases, proposed by O?cik in 1965 is extended to energetically heterogeneous solid surfaces. Other forms of this equation, more convenient in practical applications, are presented. Model calculations are made for TLC with binary mobile phases according to the modified form of O?cik's equation. Finally, this equation is compared with that of Snyder.     

Effects of solute-solvent and solvent-solvent association in liquid adsorption chromatography with binary mobile phase

Analytical equations for the capacity ratio in liquid adsorption chromatography with a binary mobile phase, involving solute-solvent and solvent-solvent association in the mobile and surface phases, have been derived. Very simple equations have been obtained for higher values of mole fraction of the more efficient eluting solvent.     

Influence of intermolecular interaction with the eluent on the retention and selectivity in liquid chromatography

Summary The influence of substance — eluent (water-isopropanol mixture) intermolecular interaction on the retention and selectivity of separation in liquid chromatography on silica gel with silanized surface has been investigated for benzene and toluene derivatives. The interaction greatly depends on the nature of the polar functional groups, their position in the benzene ring and the existence of intramolecular interaction.     

Study of open-tubular micro-capillary liquid chromatography

Capillary columns in gas chromatography, first proposed by Golay [1,2], have become well established [3] which have extremely high column efficiencies and separabilities. Everyone could imagine it to be a great tool if such a kind of high efficiency column could be established in liquid chromatography (LC). Microcapillary liquid chromatography (MCLC) may be one way of achieving high-efficiency in terms of theoretical plates. Few papers were published in this field before 1976 [4–6], but more recently, after 1977 [7–15], this field has become one of topical interest in liquid chromatography. Temporarily there are two microcapillary liquid chromatography, that is: ?open-tubular”? [7,8,10–15] and ?packed”? [9] MCLC. In this presentation we focus on open-tubular microcapillary liquid chromatography and a review contemporary developments of ours and others.     

Pneumatic pulse dampener for liquid chromatography

A simple pulse dampener is described for use with reciprocating pumps. The dampener may be assembled locally form readily available components and consists mainly of a small reservoir of compressed helium which acts as a cushion to dampen the mobile phase pulsations pneumatically. Depulsing is 99% complete and is uniform through a wide pressure range. The pneumatic dampener allows the use of single- piston reciprocating pumps in conjunction with highly flow-sensitive detectors at their highest sensitivity settings.     

Chemically-bonded chiral column packings for high-performance liquid chromatography

Summary N-Protected aminoacids have been chemically bonded to aminopropylated silica gel, and the resulting chiral phases have been applied to the LG resolution of racemic mixtures of polar compounds. Best results were obtained with surfacebound N-formyl-isoleucine and N-formylvaline, with which baseline resolutions of a range of aminoacid and aminoalcohol derivatives were achieved.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Comprehensive two-dimensional liquid chromatography

Having nearly exhausted the possibilities for generating peak capacity through improvements in column technology, chromatographers are increasingly looking to alternative ways of maximising chromatographic separation. In recent years there has been increasing activity in the field of comprehensive multidimensional separations to meet analysis demands. Comprehensive two-dimensional liquid chromatography (LC×LC) approaches offer high peak capacity which leads to significantly improved analytical performance over single-column liquid chromatography. There are several closely related avenues available for achieving an LC×LC separation and this review pays special attention to the different valve-based interfaces that have been used to comprehensively couple the first and second dimension columns in LC×LC systems. A brief discussion of column choices for selected applications and the conditions employed is also presented.     

Theoretical studies on the adsorption from non-ideal binary liquid mixtures on heterogeneous surfaces involving difference in molecular sizes of components

An equation for the phenomenon of competetive adsorption from binary liquid mixtures onto solids has been derived using the kinetic approach. In this equation the difference of the molecular sizes, the non-ideality of both bulk surface phases, and the energetic heterogeneity of the solid surface have been taken into account.

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Theoretische Untersuchungen zur Adsorption aus nichtidealen binären Lösungsmittelgemischen an heterogene Oberflächen fester Körper unter Berücksichtigung der Unterschiede in den molekularen Größen der Komponenten

Zusammenfassung Auf Grund kinetischer Erwägungen wurde eine Gleichung, die die Konkurrenzadsorption aus binären Lösungsmittelgemischen an den Oberflächen fester Körper beschreibt, aufgestellt. In der Gleichung wurde der Größenunterschied der Teilchen, die Nichtidealität der Lösung in der Volumen- und Oberflächenphase, sowie die energetische Heterogenität der Oberfläche des festen Körpers berücksichtigt.

     

Investigation of the interaction of olefin-bonded transition metal complexes by gas chromatography. II. Phosphine complexes of Cu(II)

Summary Packings consisting of chemically bonded diphenylphosphine complexes with CuCl₂ and CuBr₂ were synthesized and their retention parameters determined. The packings investigated are capable of specific interactions with electron-donating compounds and are characterized by particularly high selectivity in relation to cis and trans isomers allowing their complete separation.Part 1: see ref. [1]     

Practical applications of open tubes in liquid chromatography

The practical applications of open tubes in liquid chromatography as separation columns and as reactors for post column derivatization are discussed. With present technology, the potential efficiency of open tubular columns cannot be fully exploited. As reactors in post column derivatization, these tubes offer many advantages if knitted or stitched to enhance radial mass transfer. The application of open tubes with diameters between 0.12 mm and 0.6 mm as reactors in the selective and sensitive detection of amino acids is demonstrated.     

An isotherm equation for adsorption from binary liquid mixtures on solids involving surface heterogeneity and differences in molecular sizes of components and its numerical verification

An equation derived previously¹⁴ for adsorption from binary liquid mixtures composed of molecules of different sizes on heterogeneous solids has been reexamined. Verification of this equation by means of numerical simulation showed its applicability for describing the liquid adsorption onto weakly and strongly heterogeneous surfaces.

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Eine Isothermen-Gleichung für die Adsorption aus binären flüssigen Gemischen an heterogenen Oberflächen fester Körper unter Berücksichtigung der Differenzen in den Molekülgröen der Komponenten und ihre numerische Verifikation

Zusammenfassung Es wurde die früher¹⁴ abgeleitete Isothermen-Gleichung der Adsorption aus binären flüssigen Gemischen an heterogenen Oberflächen fester Körper abermals untersucht. Durch Computersimulation wurde gezeigt, daß diese Gleichung den obengenannten Prozeß, der sich sowohl an schwach wie auch an stark heterogenen Oberflächen vollzieht, gut beschreibt.