Liquid crystal stationary phases for gas chromatography and supercritical fluid chromatography

Abstract

Novel monomeric and polymeric liquid crystalline compounds were synthesized as stationary phases for gas chromatography (GC) and supercritical fluid chromatography (SFC). Monomeric liquid crystalline compounds were used in packed column gas chromatography for the separation of isomeric aromatic compounds and insect sex pheromones. Liquid crystalline polymers possess long nematic ranges and a uniform coating was easily achieved in glass and fused silica capillaries, which could stand temperatures up to 25OOC in GC and pressures of 200 MPa at 160OC in SFC. The columns provide excellent selectivity and resolution for fused ring aromatic compounds such as the isomers anthracene and phenanthrerie or triphenylene and chrysene.

Conformational Arrangement of Dissolved Humic Substances. Influence of Solution Composition on Association of Humic Molecules

“…TSK column (Toso Haas). The stationary phase is a rigid spherical silica gel chemically bonded with hydrophilic compounds (27) with an alleged low residual hydrophobicity and minimal ion exchange capacity. The column was preceded by a 7.5 cm TSK Guard-Column (7.5 mm i.d.)…”

Columns in analytical‐scale supercritical fluid chromatography: From traditional to unconventional chemistries

“…This adds a unique molecular shape selectivity [255], enabling the separation of positional and geometric isomers with close-boiling points [256]. The first report on liquid crystals used as stationary phase in SFC dates to 1985, when new liquid crystalline polymers were synthesized to overcome challenges connected with their use in capillary columns [256]. Sewram et al compared the selectivity of biphenylmethylpolysiloxane, polyethylene glycol, and a liquid crystalline biphenylcarboxylate ester polysiloxane in a separation of triterpene acids isolated from plants with the liquid crystal stationary phase showing the best resolution of target analytes [257].…”

“…Sewram et al compared the selectivity of biphenylmethylpolysiloxane, polyethylene glycol, and a liquid crystalline biphenylcarboxylate ester polysiloxane in a separation of triterpene acids isolated from plants with the liquid crystal stationary phase showing the best resolution of target analytes [257]. Polyacrylate liquid crystalline compounds were coated on silica and glass capillaries and tested as stationary phases for the separation of isomeric PAH [256]. However, the main drawback of liquid crystalline stationary phases was thermal instability.…”

“…Unlike conventional stationary phases separating analytes based on vapor pressure and differences in solubility, liquid crystals also reflect the arrangement of molecules forming a mesophase [254]. This adds a unique molecular shape selectivity [255], enabling the separation of positional and geometric isomers with close‐boiling points [256]. The first report on liquid crystals used as stationary phase in SFC dates to 1985, when new liquid crystalline polymers were synthesized to overcome challenges connected with their use in capillary columns [256].…”

Sample Preparation for Chromatographic Analysis

“…Retention volumes may vary unpredictably with the amount of liquid phase and the type of support used [830,831]. New phases with a polysiloxane or hydrocarbon backbone containing liquid crystal functional groups provide higher efficiency and a wider working temperature range, as well as being compatible with modern technology for preparing immobilized phases on fused silica open tubular columns [834][835][836][837][838]. At low loadings most of the stationary phase is present as a surface film and solute retention occurs largely by interfacial adsorption.…”