Eva Smolková-Keulemansová

Selected applications of cyclodextrin selectors in capillary electrophoresis.

Through the use of alpha-, beta-, gamma- and heptakis(2,6-di-O-methyl)-beta-cyclodextrin as stereospecific selectors or electrolyte modifiers, both in capillary zone electrophoresis and isotachophoresis, selected model isomeric compounds (including optical isomers) were resolved. Soluble alkylhydroxyalkylcellulose derivatives were further added to the cyclodextrin-modified background electrolytes under study. Their presence was found to be essential, as demonstrated by improvements in both enantioselectivity and separation efficiency. The results obtained in both electrophoretic modes, under optimized conditions, are compared and discussed.

Use of cyclodextrins in isotachophoresis : IV. The influence of cyclodextrins on the chiral resolution of ephedrine alkaloid enantiomers

Abstract Using β-cyclodextrin and heptakis(2,6-di-O-methyl)-β-cyclodextrin as additives to the leading electrolyte in isotachophoresis, the complete chiral resolution of pseudoephedrine antipodes was achieved, but ephedrine enantiomers were not separated. Comparative measurements with β-cyclodextrin, its dimethyl and trimethyl derivatives, demonstrated that the changes in size and hydrophobicity of the cavity collar, caused by methoxylation, substantially alter the efficiency of chiral resolution. Optimization of the isotachophoretic conditions confirmed the significant influence of the cyclodextrin concentration and pH on the separation efficiency.

Cyclodextrins as stationary phases in chromatography

Abstract Cyclodextrins and cyclodextrin polymers have been studied and applied in chromatography in recent years. Research carried out in this field is critically reviewed. The advantages of using the selective properties of these compounds for chromatographic separations and the possibilities of studying inclusion processes of different cyclodextrins with various types of substances, in the liquid as well as in the gaseous phase, are demonstrated and discussed.

Use of cyclodextrins in isotachophoresis: VII. Resolution of structurally related and chiral phenothiazines

Commercially available phenothiazine derivatives were used for the study of cyclodextrin complex formation by cationic isotachophoresis with alpha-, beta- and gamma-cyclodextrin and methylated analogues of beta-cyclodextrin as leading electrolyte additives. The relationships between the type of solute substituent in the 10- and/or 2-position and the stability of the created cyclodextrin complex were studied and the results were utilized for the optimization of isotachophoretic conditions suitable for the resolution of the studied phenothiazine derivatives. Successful resolution of three racemic solutes was achieved.

Cyclodextrins and methylated cyclodextrins as stationary phases in gas-solid chromatography

Abstract Cyclodextrins and their methylated derivatives were used as stationary phases in gas-solid chromatography and the effect of inclusion on the retention of compounds with various structures and geometries (alkanes, aromatic hydrocarbons, alcohols) was followed. It has been found that inclusion predominates in the gas-solid interaction of compounds with suitable geometric dimensions, while the retention of polar substances is primarily determined by the interactions with the cyclodextrin hydroxyl groups. On decreasing the cyclodextrin polarity by means of methylation, stereoselectivity was evident even in the separation of alcohols. On the other hand, the presence of methyl groups causes steric hindrance to penetration of the guest molecule into the cyclodextrin cavity. The selectivity of the inclusion process is especially important for separations of positional isomers.

Inclusion compounds in chromatography

Abstract This review summarizes the present knowledge on inclusion compounds in general and on the application of their specific properties in analytical chemistry, especially in chromatography. The use of various inclusion compounds in liquid-liquid, gas-liquid, gas-solid, gel permeation and thin-layer chromatography for analytical purposes and the possibility of studying inclusion compounds chromatographically are discussed.

Use of cyclodextrins in isotachophoresis : II. α, β and γ-cyclodextrins as leading electrolyte additives for the separation of ortho-, meta- and para-substituted halogenobenzoic acids

Abstract The influence of α-, β- and γ-cyclodextrins on the isotachophoretic separation of ortho -, meta - and para -substituted halogenobenzoic acids was studied. Cyclodextrins were added to a conventional leading electrolyte. Unambigous relationships between the size and position of the substituent, the cavity diameter and the stability of the cyclodextrin complex formed were obtained. The complex formation with the cyclodextrins leads to an improvement in the separation of isomers.

Use of cyclodextrins in isotachophoresis : VI. Cyclodextrins as leading electrolyte additives for the separation of bile acids

Cyclodextrins (CDs) and some of their methyl derivatives have been used for the optimization of the isotachophoretic separation of bile acids in aqueous electrolyte systems. The addition of heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin to the leading electrolyte proved useful for both the solubilization and the structural differentiation of the solutes studied and led to the successful separation of their mixtures. Other CDs tested, even if they gave a satisfactory solubilization effect, did not support the resolution of bile acid mixtures.

Chromatographic study of the inclusion properties of cyclodextrins: Study of inclusion from the gaseous phase

The ability of cyclodextrins to form inclusion compounds with substances in the gaseous phase was studied chromatographically. Chromatographic measurements enabled the mechanism of the inclusion process to be clarified and have shown that other forces, mainly hydrogen bonding, play a role in the process in addition to the geometric properties of the interacting substances. These facts are expressed in terms of the changes in the chromatographic quantities and of the changes in the thermodynamic characteristics that are derived from the former quantities. The selective properties of cyclodextrins have been utilized in separations of substances that are otherwise separated with difficulty (xylenes, diethylbenzenes, trimethylbenzenes, etc.).

Comparative studies of the chromatographic properties of α- and β-cyclodextrin in gas-solid and gas-liquid chromatography

Abstract A systematic study was carried out of the properties of α- and β-cyclodextrins as selective agents for the separation of various compounds, mainly isomers, in gas-liquid and gas-solid chromatographic systems. The test compounds included aliphatic and aromatic hydrocarbons (xylenes, trimethylbenzenes, diethylbenzenes) and alcohols (propanols, butanols). The possible interaction mechanism is discussed in terms of molecular inclusion, the effect of the nature of the matrix solvent on the chromatographic properties of the cyclodextrin solutions and the selectivity due to the inclusion process. Examples of chromatographic separations are given.