E. Smolková

Study of the properties of cyclodextrins as stationary phases in gas chromatograpy

Abstract The formation and properties of inclusion compounds of α- and β-cyclodextrin were studied in a gas-solid chromatographic system. Substances of various structural types and geometries (hydrocarbons, hydrocarbon halogeno derivatives, alcohols, aromatic compounds) were used as sorbates. The results of chromatographic measurements are correlated with polarizability and polarity data for the sorbate molecules, and interpreted in terms of the possible interactions involved.

Comparison of linear and branched non-polar chemically bonded stationary phases in high-performance liquid chromatography

Non-polar chemically bonded stationary phases having branched or unbranched structure were synthesized, and their specific surface areas, pore size distributions and carbon contents were estimated. Based on these data the number of silane molecules bonded to unit surface area of the original silica was calculated for each phase. Retentions of selected solute groups were measured in four mobile phases of various elution strength, prepared from methanol-water mixtures at various ratios. Dependences of k′ on the length of the “bristle”, on the size and structure of solute molecule and the elution strength of mobile phase were plotted. Results are compared for pairs of phases having different structures but either the same total number of carbon atoms in the bonded molecule or the same length of the “bristle”.

A PTFE-based carbon adsorbent in high-performance liquid chromatography

Abstract A new type of carbon adsorbent, prepared by reduction of PTFE, was studied and modified with the aim of obtaining a material with a relatively homogeneous, non-polar surface for applications in high-performance liquid chromatography. Three types of sorbent differing in the specific surface area, oxygen remainder and porosity were investigated. The chromatographic behaviour of various solutes, both in non-polar (e.g., pentane) and polar (aqueous buffer) media, has been studied. The plots of natural logarithm of the capacity factor vs. the carbon number were reasonably parallel for a homologous series with different functional groups. The influence of the ionization of some amino acids on their retention over the whole pH range has been shown.

Gas chromatography of 3H- and 14C-labelled compounds.

Abstract GC methods of analysis of 3H- and 14C-labelled compounds that have been published in the period from 1955 to mid-1976, together with important applications, are reviewed. In addition to its obvious use for identification purposes, RGC is mostly used for the determination of the distribution of radioactivity among the components of mixture under analysis and for the determination of their contents and specific activities. It can be also combined with chemical reactions (reaction gas chromatography). Applications that require derivatization have some limitations connected with the derivatization reaction and the stability of the derivatives. The separation of isotopic molecules by GC is also possible. For the measurement of radioactivity, a discontinuous method involving the collection of fractions and subsequent counting is often used, while for continuous monitoring of effluent activity flow-through radiation detectors (Geiger-Muller and proportional counters, ionization chambers and scintillation methods) are used, mainly after conversion of the effluent. The possibilities of various recording techniques with respect to quantitative evaluation are surveyed and applications of RGC in the production of labelled compounds,“hot-atom” chemistry, organic chemistry, chemical processing, biochemistry and clinical chemistry are discussed.

Gas-liquid chromatographic analysis of trimethylsilyl derivatives of pyrimidine and purine bases and nucleosides

A systematic study of basic nucleic acid components and their biologically significant derivatives has been carried out. The optimum silylation conditions have been found and the chromatographic behaviour of the trimethylsilyl derivatives formed has been studied. Relations between the gas chromatographic behaviour and the structure of the substances analyzed were investigated on the basis of the retention indices measured on two stationary phases of different polarity. The relative molar responses were determined for the quantitative determination of the substances. The results make possible the determination of biologically active substances in pharmaceuticals.

High-performance liquid chromatographic behaviour of N-substituted phthalimides : Calculation of capacity factors for members of the homologous series☆

Abstract The high-performance liquid chromatographic behaviour of some N-substituted phthalimides on normal and reversed-phase columns was studied. The retention of the compounds is discussed in terms of shielding of the polar CONCO group of phthalimide by non-polar or slightly polar substituents. The linear dependence of log k′ on the number of carbon atoms of the alkyl substituent of N-alkylphthalimides has been used as a basis for deriving a general formula for calculating the capacity factor for any member in the homologous series.

Importance and use of inclusion compound formation in gas—solid chromatography

Abstract Gas chromatography can supply useful information on the course of clathration and the formation of inclusion compounds can be utilized in the chromatographic separation of substances. In aaddition to the interactions common in gas—solid and gas—liquid chromatographic systems, specific properties of inclusion compounds play a role and can sometimes be used with advantage for analytical purposes. Systems containing wide-pore silica (Silochrom S-80) or Chromosorb W coated with urea or thiourea as hosts were investigated. The measurements were carried out by using sorbates selected on the basis of their clathrating ability. The temperature dependence of V9 was determined over the temperature range 40–140° on a mono-molecular layer of urea on silica. Comparison of the retention data on pure silica and Chromosorb W and on these substances coated with urea or thiourea indicated that the formation of inclusion compounds contributes to the retention of sorbates that are capable of clathration. Although this process is less pronounced in the gaseous phase than in the liquid phase, it is still advantageous for certain types of substances. that can be analysed very rapidly, in short columns and at lower tempertures than on common chromatographic packings.

Gas chromatographic separations of alkanes of urea inclusion compounds with n-alkanes as stationary phases

Abstract Urea adducts with n -octane, n -decane, n -dodecane, n -tetradecane and n -hexadecane have been studied as stationary phases in gas chromatography. With all the adducts examined, selective sorption of n -alkanes and of branched alkanes with a single methyl group in the side-chain was found. This sorption is caused by the presence of hexagonal channels with a diameter of 5 A in the adduct inclusion structure. All factors that increase the dissociation, i.e. temperature or the content of the guest molecules, increase the adduct selectivity. On the other hand, all factors that suppress the dissociation, i.e. the chain length of the guest molecules and the vapour pressure of the guest molecules, decrease the selectivity. The sorption properties of the adducts were utilized for the separation of model alkane mixtures.

A study of the sorption properties of the “spherosils”

Abstract Spherosil (with the commercial name “Porasil”) is one of the most specific adsorbents and its application is widened by its use in gas chromatography. It is based on porous silica beads, and is able, because of the hydroxyl groups on its surface, its sorption character, the behaviour of benzene, n-hexane and cyclohexane was followed, i.e., thta of sorbates with the same number of carbon atoms but with different structures. Attention was paid to the activation conditions and to the dependence of the sorption character on changes in specific surface area. It was important to decide to what degree the concentration of the surface hydroxyl groups varies with changes in the specific surface area. The measurement and evaluation of adsorption isotherms were carried out by the frontal chromatographic technique, using Spherosils with four different surface areas. It is concluded from the calculated absolute adsorption isotherm that, in the series of Spherosils studied, a change in the geometrical surface area and possibly in the porosity play a predominant role while the concentration of hydroxyl groups on the surface is approximately constant.

Adsorption properties of thermally pretreated porasils

SummaryA simple modification was employed by thermal or hydrothermal treatment of silica gel (Porasil). In this way chromatographic materials with advantageous properties were prepared. The changes of the adsorbent under different thermal and hydrothermal treatment were studied in more detail. The experimental results show that under controlled conditions material with required chromatographic properties can be prepared.