Conventional Stationary Phases Research Articles

Direct aqueous injection gas chromatography on a potassium fluoride crystal hydrate-containing sorbent: Determination of volatile organic solvents in the fermentation broth of Clostridium strains

For the direct aqueous injection gas chromatographic determination of volatile organic solvents (acetone, ethanol, butanol) in culture spent media of Clostridium acetobutilicum, a sorbent which contains potassium fluoride crystal hydrate and a conventional stationary phase, Triton X-305, is used. Analysis is carried out using a stainless-steel column packed with the developed sorbent. The total time of analysis is less than 5 minutes at a column temperature of 65°. The column is stable for at least 1 year.

Direct aqueous injection gas chromatographic analysis of polar compounds using sorbents containing potassium fluoride dihydrate

For direct aqueous injection gas-chromatographic analysis of polar compounds present in aqueous solutions sorbents containing conventional stationary phases and potassium fluoride crystal hydrate are proposed. On such sorbents polar compounds elute with narrow symmetrical zones under gentle chromatographic conditions. In such sorbents KF.2H2O mainly deactivates the surface of the solid support. The polarity of these sorbents is compared with the polarity of molten potassium fluoride dihydrate and conventional stationary phases.

Evaluation of new organoclay stationary phases for the separation of ethylbenzene and xylene isomers

Several kinds of Bentones which have structures similar to Bentone 34 have been tested and compared for the purpose of improving the resolution of ethylbenzene and xylene isomers by gas chromatography. Bentone SD-3 was found to have higher selectivity toward these close-boiling compounds than the well known stationary phase Bentone 34. Modification effects of some conventional stationary phases which represent the whole range of polarity on the chromatographic property of Bentone SD-3 have been investigated and discussed. A number of new organoclays which have different structures of the organic cation in complexes have been synthesized and their properties evaluated for the separation of positional isomers. A simultaneously high selective organoclay for each component in the aromatic mixture of ethylbenzene and xylene isomers, without assistance of conventional stationary phases, has been described.

Comparison of methods for the determination of the polarity and selectivity of stationary phases in gas chromatography from a thermodynamic point of view

Different scales proposed for the evaluation of polarity and selectivity in gas chromatography as relative and absolute values were compared. It is shown that the scale including six parameters, Δ G( X), Δ G( Y), Δ G( Z), Δ G( U), Δ G( S), and Δ G(CH 2), is more suitable and allows a unified system to be obtained for the polarity and selectivity of conventional stationary phases, organic and inorganic salts and polymer sorbents. The main equation for the calculation of the partial molar free energy of sorption, Δ G, is simplified for capillary gas chromatography.

Unexpected elution behaviour of peptides with various reversed-phase columns

Gastrin and cholecystokinin peptides were separated by reversed-phase chromatography on conventional bristle-type and polymer-coated stationary phases. The retention of the sulphated and non-sulphated isomeric forms of both peptides is governed by the structure of the peptide, the net charge and additional polar interactions with the stationary phases. Polymer-coated phases are optimum for separations according to chain length, whereas polar interactions are required for the separation of sulphated and non-sulphated peptides of identical chain length.

The effect of elevated temperature on conventional stationary phases used in SFC

The effect of elevated temperatures on conventional packed bonded-phase columns used in supercritical-fluid chromatography (SFC) has been investigated. The impact of column conditioning temperature on the capacity factor, peak width, and peak asymmetry on octadecyl and propylamino columns from five commerical suppliers is reported.

Thermodynamic evaluation of the intermolecular interactions of potassium fluoride crystal dihydrate in gas chromatography

Potassium fluoride crystal dihydrate is used as the stationary phase for the rapid analysis of polar compounds in aqueous solutions. KF·2H2O is compared with some conventional stationary phases, organic salts and molten crystal hydrates of inorganic salts.

New liquid crystalline stationary phase for capillary gas chromatography

In the last few years the use of capillary columns with liquid crystalline stationary phases has increased. In general, liquid crystals are stationary phases of medium polarity, therefore a mixed retention mechanism is expected]. It is known that the surface of the support affects the orientation of the molecules of the liquid crystalline stationary phase and that this effect is greater than with conventional stationary phase+. Recently we have systematically studied the influence of the film thickness and the surface quality on the properties of selected liquid crystalline stationary phases coated on glass capillary columns, and on the retention data of compounds having different structures and polarities3. The aim of this work was the introduction of a new, more polar, liquid crystalline stationary phase and to compare its properties in capillary columns with that of comparable structure.

Prospectives of polymeric liquid crystal stationary phases for capillary column gas chromatographic separations

The liquid crystalline polysiloxane substrate offers unique selectivity when used in capillary column gas chromatography. The separation and identification of priority pollutants along with other compounds is very difficult but important. In particular, the separation of isomeric organic compounds having similar volatilities could not be obtained on capillary columns using conventional stationary phases. The complete separation of ortho, meta, and para isomers of certain disubstituted benzenes as well as polycyclic aromatic compounds was achieved on a capillary column using a liquid crystalline polysiloxane stationary phase. The complete separation of octachlorodibenzodioxin from octachlorodibenzofuran was also obtained on this column which is not possible on columns of identical lengths using conventional stationary phases. The separation of polycyclic aromatic compounds in a complex sample of airborne particulate matter extract on the liquid crystal column is demonstrated.

Selectivity and chemical structure of nematic mesophases in gas chromatography

The retention behaviour of geometrical isomers and Rohrschneider compounds was measured in the nematic range of liquid crystalline stationary phases having different chemical structures, in order to determine the influence of these structures on the polarity and selectivity of the phases. It was found that lateral substituents in mesogenic molecules effect a change in selectivity. The polarities of these phases are compared with those of conventional stationary phases, and the strong influence of the terminal groups of the liquid crystal molecules on Δ I values is discussed.

Free radical cross-linking in the preparation of non-extractable stationay phases for capillary gas chromatography

Free radical cross-linking of methylpolysiloxane stationary phases to form insoluble rubbers recently became of widespread interest in capillary column gas chromatography. The use of various peroxides as free radical generators to form carbon—carbon cross-links in conventional stationary phases has been reported. In this study the applicability of various peroxids and azo compounds fro free radical cross-linking and the effects that these free radical generators have on commercially available stationary phases are described. Characteristics of the stationary phases such as chain length and functional groups and their roles in the cross-linking mechanism are discussed. The properties of benzoyl peroxide, dichlorobenzoyl peroxide, dicumyl peroxide, tert.-butylperoxide, and azo- tert.-butane as free radical generators were evaluated. Stationary-phase polarity change, column activity change and loss of stationary phase were all considered in the overall evaluation of the effectiveness of these free radical generators. Azo- tert.-butane showed minimal effect on phase polarity and column activity while benzoyl peroxide and dicumyl peroxide were the most effective in forming insoluble stationary phases.

Liquid crystals : III. application of laterally substituted liquid crystals for the separation of alkylbenzenes compared with conventional stationary phases in gas chromatography

The retention behaviours of 26 alkylbenzenes on a laterally substituted liquid crystalline stationary phase and on conventional stationary phases in gas chromatography have been compared. Elution of alkylbenzenes in the nematic state of liquid crystalline substrates is dependent on the linearity and planarity of the probe molecules, whereas on conventional stationary phases they elute on the basis of their boiling points. The relative retention values (α) for close-boiling positional isomers on conventional stationary phases are near unity, but their separation can be achieved on liquid crystalline substrates. The variation of the relative retention value with respect to the chain length of the alkyl substituents is discussed.

Methylated cycloamyloses (cyclodextrins) and their inclusion properties

2,3,6-Tri- O-methyl and 2,6-di- O-methyl derivatives of cyclohexa- and cyclo-hepta-amylose (2,3,6-tri- O-methyl- and 2,6-di- O-methyl-α- and -β-cyclodextrin) have been prepared and shown to be versatile complexing agents. Their complexes in aqueous solution are usually more stable than the corresponding complexes of un-substituted cycloamyloses. The methylated cycloamyloses also form crystalline complexes, the stability of which depends on the size and shape of the guest molecule. The decomposition temperature of the crystalline complexes with homologous n-alkanes, which is relatively high increases with increasing chain-length of the hydro-carbon. The shift of the i.r. carbonyl band of oleic acid in its solid complex with methylated α-cyclodextrin probably reflects inclusion of the fatty acid in the mono-meric form. The methylated cycloamyloses, when used as the stationary phases for g.l.c. or dissolved in a conventional stationary phase, affect the retention times of organic compounds in a manner which suggests that inclusion phenomena are operative.

Gas chroamtographic separation of optically active compounds in glass capillaries

Chiral compounds may be separated by gas chromatography by direct enantiomer separation on optically active stationary phases. More generally the separation can be achieved on conventional stationary phases after formation of diastereoisomeric derivatives. In this work we report on new results in enantiomer separation, indicating that hydrogen bond association is not the only kind of molecular interaction responsible for enantiomer separation. For the separation of a wide variety of chiral compounds with amino or hydroxy groups diastereo-isomeric derivatives may be formed by reaction with L-α-chlorisovaleryl chloride. The derivatives of amino acids, aliphatic and aromatic amines, amino alcohols and of some alcohols are separated in glass capillaries. Gas chromatography as a separation technique of high selectivity is specifically useful for the separation of mixtures of chemically related components with comparable molecular interactions with the molecules of the stationary phase of a gas chromatographic column. The separation of optically active compounds, particularly, requires highly efficient columns. Glass capillary chromatography is a tool that meets this standard and was applied exclusively in this work.