Jiří Snopek

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.

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.

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.

Concept of effective and non-effective inclusion complex formation in isotachophoresis

Abstract On the basis of experimental experiences, a simple mathematical model of 1:1 cyclodextrin-solute complex formation is proposed. A possible role of two limiting cyclodextrin-solute interactions, introduced as effective and non-effective complex formation, on the quality of isotachophoretic resolution has been studied and is discussed. Additional parameters, e.g., the solute molecular weight, its effective charge and the molecular weight of the cyclodextrin used, are involved in the proposed model. Their influence on the isotachophoretic separation was estimated by comparing the computer simulated mobility ratio curves of cyclodextrin-complexed solutes obtained at various values of the corresponding parameters.

Influence of counter-ion inclusion complexation on the quality of cyclodextrin-supported separations in isotachophoresis

Abstract The effect of counter-ion inclusion complex formation on the separation efficiency in electrolyte systems modified with β-cyclodextrin and its methyl derivatives was studied. On the basis of the analysis of complex-forming equilibria established in the sample mixed zone, it was concluded that an increasing stability of the counter-ion inclusion complex results n a decreased efficiency of the separation process. This was verified experimentally on the set of eleven aliphatic and aromatic acids used as counter-ions in slightly acidic cationic electrolyte systems.