Evaluation of smectic biphenylcarboxylate ester liquid-crystalline polysiloxane stationary phases for capillary column gas chromatography

Mesomorphic biphenylcarboxylate esters were coupled via flexible aliphatic hydrocarbon spacers to a polysiloxane backbone. The influence of spacer length, percent mesomorphic substitution, and crosslinking of the stationary phase on liquid-crystalline transition temperatures and on chromatographic performance was investigated. Unique selectivity and good efficiency over a wide temperature range for gum and cross-linked liquid-crystalline phases were demonstrated by the separation of various isomeric polycyclic aromatic compounds.     

Polarizable biphenyl polysiloxane stationary phase for capillary column gas chromatography

A crosslinkable biphenylmethylpolysiloxane stationary phase was synthesized for capillary column gas chromatography and compared with methyl, phenyl, and cyanopropyl polysiloxane stationary phases for the separation of isomeric polycyclic aromatic compounds. While the new phase gave similar separations of nonpolar isomers when compared to the nonpolar phases, separations of polar isomers were greatly improved because of the induced polarity of the biphenyl group of the stationary phase by the solute molecules. This polarizable stationary phase offers a unique selectivity which is not available in other stationary phases.     

Nonextractable cyanopropyl polysiloxane stationary phases for capillary chromatography

Summary Crosslinkable cyanopropylpolysiloxane stationary phases have been difficult to produce because of steric effects of the large cyanopropyl groups or because of the interaction between the polar cyanopropyl groups and the groups added for crosslinking. Various polymers containing 50% to 90% cyanopropyl were synthesized which contained vinyl,p-tolyl, or 4-vinylphenyl groups for crosslinking. Thep-tolyl group was found to give satisfactory crosslinking if there were two such groups attached to one silicon atom.     

Preparation and study of two polysiloxanes with pendant hand-basket type calixarene stationary phases for capillary gas chromatography

In this study two novel pendant hand-basket type calixarene gas chromatography stationary phases were prepared by hydrosilylation of ω-undecenyloxymethyl dimethyl calix[4]-15C5 and ω-undecenyloxymethyl dimethyl calix[4]-18C6 with dichloromethane followed by condensation reaction with silanol-terminated polydimethylsiloxane. Important stationary phase properties of these two novel stationary phases such as column efficiency, polarity, and selectivity were examined and compared with those of ω-undecyloxymethyl-18-crown-6, 2,3-benzo-9-propyloxymethyl-15-crown-5 and 2,3-benzo-11-propyloxymethyl-18-crown-6. Excellent thermostability from 60 to 330°C with onset bleeding temperatures at 308°C have been found. The mechanism of specific selectivity for position isomers based on the calix[4]crown ether ring, the molecular size of the solute and its shape are discussed.     

Synthesis of siloxane stationary phases for capillary gas chromatography and supercritical fluid chromatography

A comparison is made between dichlorosilanes and cyclic siloxanes as starting materials in the synthesis of stationary phases for capillary gas chromatography (CGC) and supercritical fluid chromatography (SFC). Siloxanes containing one or more of the side groups methyl, vinyl, phenyl, and cyanoethyl in various ratios were synthesized and compared. These phases were characterized by chromatographic (gel permeation, GPC), spectroscopic (IR, ¹H NMR, ²⁹Si NMR), and thermal (DSC) methods. Coated fused silica columns were evaluated with respect to polarity, crosslinkability with several free-radical initiators, and thermal stability. A new liquid phase, 7% cyanoethyl, 7% phenyl, 1% vinyl methyl polysiloxane is shown to be more polar than OV-1701, more temperature stable, easily crosslinked and suitable for use in supercritical fluid chromatography.     

Liquid-crystalline stationary phases for gas chromatography

Physico-chemical properties of new liquid-crystalline stationary phases (LCSPs) for gas chromatography are reviewed. The mechanism of chromatographic separation on liquid-crystalline stationary phases is discussed and examples of analyses of complex mixtures of organic compounds using capillary and packed columns are given.     

Preparation and chromatographic characteristics of calix[4]arene polysiloxane as stationary phases for capillary gas chromatography

Summary Two new kinds of calix[4]arene derivatives, 5, 11, 17, 23-tetra-tert-butyl-25,27-bis(isopropylcarbamoyl-methoxy)-26,28-diundecenyloxy calix[4]arene (C[4]A) and 25,27-dibutoxy-5, 11, 17, 23-tetra-tert-butyl-26,28-diundecenyloxy calix[4]arene (C[4]B0, are prepared and then are polymized by two different processes. Three calix[4]arene polysiloxane stationary phases for capillary gas chromatography are obtained. Their chromatographic characteristics, including column efficiency, polarity, selectivity, glass-transition temperature and thermal stability are studied. Retention mechanisms are also discussed.     

Ionic liquid‐bonded polysiloxane as stationary phase for capillary gas chromatography

Ionic liquid (IL) stationary phase is especially suitable for separation of complex samples, owing to the “dual nature” of IL. In this study, a synthetic method of ionic liquid‐bonded polysiloxane (PSOIL) as stationary phase of GC was proposed. Then, the PSOIL was used to prepare an 8 m capillary column by static method. The column efficiency was measured to be about 4000 plates/m (k=3.55, naphthalene) after the column had been conditioned at 210°C. The durability of PSOIL column was better than that of the mixed stationary phase of IL and OV‐1. Moreover, the Abraham solvation parameter model was employed to characterize the PSOIL. The result revealed that the PSOIL had stronger dispersion force (l) than neat IL and stronger hydrogen bond basicity (a) than DB‐1. That meant the PSOIL might offer good selectivity for both polar and non‐polar analytes. The column exhibited unique selectivity for various organic substances, such as the homologous compounds of alkanes, esters, alcohols and aromatic compounds. It was also found that some aromatic positional isomers could be separated better on the PSOIL column than on the DB‐1 column. Furthermore, the stationary phase was suitable for separation of high‐boiling point compounds such as polycyclic aromatic hydrocarbons, phthalic esters, etc. All of these demonstrated that the PSOIL offered good selectivity and high separation efficiency for a wide range of analytes.     

Autocrosslinkable methyl-2-phenylethylpolysiloxane stationary phase for capillary column gas chromatography

Methyl-2-phenylethylpolysiloxane polymers have been synthesized for comparison with methylphenylpolysiloxane stationary phases for gas chromatography. The 50% 2-phenylethyl polysiloxane was found to be autocrosslinkable at 260°C without addition of free redical initiator. Although the selectivity of this phase appears to be similar to the 50% phenyl polysiloxane, its thermal stability is not as high.     

Ionic liquid stationary phases for gas chromatography

This article provides a summary of the development of ionic liquids as stationary phases for gas chromatography beginning with early work on packed columns that established details of the retention mechanism and established working methods to characterize selectivity differences compared with molecular stationary phases through the modern development of multi-centered cation and cross-linked ionic liquids for high-temperature applications in capillary gas chromatography. Since there are many reviews on ionic liquids dealing with all aspects of their chemical and physical properties, the emphasis in this article is placed on the role of gas chromatography played in the design of ionic liquids of low melting point, high thermal stability, high viscosity, and variable selectivity for separations. Ionic liquids provide unprecedented opportunities for extending the selectivity range and temperature-operating range of columns for gas chromatography, an area of separation science that has otherwise been almost stagnant for over a decade.     

Use of crosslinked polysiloxane stationary phases in open-tubular capillary liquid chromatography

Crosslinked polysiloxane stationary phases were prepared on soda-lime glass capillaries and applied to the separation of polynuclear aromatic hydrocarbons and of phthalates in reversedphase liquid chromatography. Preparation procedures and chromatographic performance of these columns are described.     

Novel stationary phases based on asphaltenes for gas chromatography

We present the results of investigations on the possibility of the application of the asphaltene fraction isolated from the oxidized residue from vacuum distillation of crude oil as a stationary phase for gas chromatography. The results of the investigation revealed that the asphaltene stationary phases can find use for the separation of a wide range of volatile organic compounds. The experimental values of Rohrschneider/McReynolds constants characterize the asphaltenes as stationary phases of medium polarity and selectivity similar to commercially available phases based on alkyl phthalates. Isolation of asphaltenes from the material obtained under controlled process conditions allows the production of a stationary phase having reproducible sorption properties and chromatographic columns having the same selectivity. Unique selectivity and high thermal stability make asphaltenes attractive as a material for stationary phases for gas chromatography. A low production cost from a readily available raw material (oxidized petroleum bitumens) is an important economic factor in case of application of the asphaltene stationary phases for preparative and process separations.     

Cyclodextrin dimer derivatives used as stationary phase for capillary gas chromatography

Summary Four cyclodetrin dimer derivatives were synthesized by linking two single cyclodextrin derivatives with difunctional spacer at the primary side of cyclodetrin. The separation properties of these cylodextrin dimer derivatives as CGC stationary phases were investigated and compared with those of the unbridged native cyclodextrin derivative. The results show that two recognition sites and one link spacer of these cyclodextrin dimer derivatives cooperate in separation and affect the separation of disubstituted benzene positional isomers.     

Dicyanobiphenyl polysioloxane stationary phases for capillary column gas chromatography

Summary The chromatographic performance of newly developed dicyanobiphenyl polysiloxane stationary phases were evaluated and compared with the performance of other polar stationary phases, including the previously reported monocyanobiphenyl polysiloxanes. Due to the unique combination of polarizable biphenyl and polar cyano functionalities in the side chains of the flexible polysiloxane backbone, and by virtue of their mild liquid crystalline properties, the new stationary phases provide excellent resolution of a wide variety of analytes, both polar and nonpolar, in both GC and SFC. They can be easily coated and cross-linked in open tubular columns, and the resultant columns demonstrate excellent efficiency and performance at temperatures up to 280–300°C. The new stationary phases exhibit enhanced selectivities for various types of isomeric compounds.     

Capillary column coated with graphene oxide as stationary phase for gas chromatography

The graphene oxide (GO) is carbon based material that has high surface area, high adsorption ability, and is stable at high temperature. In this work, the GO phase was prepared and used for gas chromatographic separation. GO nanosheets were covalently bonded onto the inner surface of fused silica capillary column using 3-aminopropyldiethoxymethyl silane as cross-linking agent. The prepared GO nanosheets were characterized with TEM and the GO coating was characterized with SEM. As a high performance stationary phase, GO provides not only a high surface area to increase the phase ratio but also rich functional groups for the formation of hydrophobicity, hydrogen bonding, and π–π electrostatic stacking interactions with volatile aromatic or unsaturated organic compounds. Thus, mixtures of a wide range of organic compounds including alcohols and aromatic compounds were well separated and an efficiency of 1990 theoretical plates per meter for anisole was obtained on GO coated 1.0 m × 200 μm i.d. fused silica capillary column. The experimental results demonstrate that GO coated capillary columns are promising for gas chromatographic separation.     

A novel ionic liquids grafted polysiloxane for capillary gas chromatography

A new ionic liquids grafted polysiloxane used as stationary phase for capillary gas chromatography(CGC) is described.The stationary phase of 1-vinyl-3-hexylimidazolium hexafluorophosphate anchored to polysiloxane(PMHS-[VHIm][PF_6]) was synthesized, characterized and coated onto capillary columns by static coating.The results show that the present stationary phase exhibits a very good chromatographic resolution and selectivity for Grob test mixture and alcohols with baseline resolution and symmetry peaks....     

Effect of viscosity on stationary phase stability in capillary column gas chromatography

With recent advances in column technology it is now possible to prepare highly efficient, very inert, and thermally stable capillary columns coated with nonpolar polysiloxane stationary phases. Unfortunately, the same degree of success has not been achieved for some of the more polar polysiloxane phases. A parameter that has been studied little in the past in relation to stationary phase film stability is the viscosity of the stationary phase. In this paper the efficiency and stability of coated columns are correlated to the viscosity of the phase. Due to their structure, the viscosity of the phenyl-containing polysiloxanes change rapidly with temperature and hence, thin-film coatings are not stable at elevated temperatures. By using high viscosity phenyl-containing methylphenylpolysiloxanes which were recently synthesized, efficient and stable columns have been prepared.     

The effect of the trifluoropropyl group in polysiloxane stationary phases used for capillary gas chromatography

Four poly(methyl 3,3,3-trifluoropropyl siloxanes) with trifluoro-propyl group content (group substitution) between 8 and 35 percent have been synthesized and characterized as stationary phases for gas chromatography in borosilicate glass capillary columns. Results are compared with those from two commercial stationary phases–a polydimethylsiloxane and a poly(methyl 3,3,3-trifluoropropyl siloxane) with a fifty percent trifluoropropyl group content (group substitution). Retention index values, McReynolds constants, polarity (as defined by McReynolds) and retention polarity (as defined by Takács) increase regularly with the trifluoropropyl group content of the stationary phase. The temperature coefficient of the retention indices of the McReynolds probes, and that of the polarities, have been determined at temperatures between 60 and 180 °C. Specific retention volumes do not follow the linear dependence on trifluoropropyl group content observed for retention indices or polarities. Substances with electron-donor groups show maximum retention for a trifluoropropyl group content of ca 30%, whereas the retention of hydrocarbons, halogenated compounds, and alcohols decreases as the degree of trifluoropropyl group substitution increases from 0 to 50%. It is felt that a polysiloxane with a trifluoropropyl group content of ca 30 to 35% would be the best choice for the separation of ketones, nitro compounds or amines.     

The selectivity of crown ether polysiloxane stationary phases

Summary The phase recognition mechanism of nine groups of position isomers on four crown ether polysiloxanes, OV-1701 and PEG 20M has been investigsated by measuring various thermodynamic parameters. The high selectivity of crown ether polysiloxane phases is due to hydrogen bonding and the extent of fitting between the analytes and the crown ethe cavity. The effects on selectivity of cavity size, heteroatoms and substituent groups on the crown ether are discussed.     

Gas chromatography in qualitative analysis Part 16. An investigation of the oxidation of reference stationary phases used in column characterization by the Rohrschneider and McReynolds methods

Summary The on-column oxidation of hydrocarbons commonly used as stationary phases in column characterization is investigated. In each case significant shifts of retention are observed, which may be negative or positive depending upon the polarity of the test solutes and the adsorptivity of the support material. In order to reduce the consequent uncertainties in the Rohrschneider [1] and McReynolds [2] polarity values, a new method of column characterization is proposed. The applicability of the new method is illustrated by a consideration of a range of silicone liquid phases.