The comparative gas chromatographic behavior has been investigated for lwo new Jiquidcrystal stationary phases, 2-(3-chlorobenzyloxy)-3-hexanoxy-4-(4-chlorobenzoyloxy)-4'-(4methylbenzoyloxy)azobenzene (denoted 3-CI) and 2-(3-methylbenzyloxy)-3-hexanoxy-4-(4chlorobenzoyloxy)-4'-(4-methylbenzoyloxy)azobenzene (denoted 3-CH3). The structures of the main core of the f,,vo liquid crystals are the same but they differ by lateral aromatic branch -3-chlorobenzyloxy and 3-methylbenzoyloxy. Their thermal properties were established by use of differential scanning calorimetry (DSC) and their chromatographic separation properties by use of glass capillary columns. Interesting analytical performance was obtained in the separation of isomeric aromatic compounds, polyaromatic compounds, volatile aroma compounds, and cis and trans isomers. Separation efficiency was hig her for 3-CI, especially for volatile aroma compounds, light aromatic compounds, and polyaromatic compounds, although the phases were similar in otherways.
Key WardsGas-liquid chromatography Liquid crystal mixtures as stationary phases Differential scanning calorimetry Aromatic hydrocarbons and phenols SummaryThe thermal and chromatographic properties of an equimolecular mixtu re of I',,vo liquid crystals have been investigated. Differential scanning calorimetry showed that the clearing temperature of the mixture is intermediate bel',,veen the corresponding temperatures for the individual liquid crystals. The melting temperature was lower than the corresponding temperatures for the separate liquid crystals. Polarizing microscopy showed that the liquid crystal phase of the mixture was nematic. The analytical performance of the mixed liquid crystal was investigated by use of different kinds of solute (aromatic hydrocarbons, polycychc hydrocarbons, phenols, volatile aroma compounds). It seemed that the behavior of the nematic mixture was the same as that of a pure nematic liquid crystal.When separations were performed with the mixture the more elongated isomer (para for positional isomers, trans for geometric isomers) was the most retained solute.
Study of nomadic new liquid crystals with lateral chain by gas chromatography. The analytic performances of three stationary phases 'liquid crystal' to side chain have been presented. Mesogenic compounds studied in this work are: -3-CH 3 : 2-(3-methylbenzyloxy)-3-n-hexyloxy-4-(4-chlorobenzoyloxy)-4'-(4-methyl benzoyloxy)-azobenzene; -4-CH 3 : 2-(4-methylbenzyloxy)-3-n-hexyloxy-4-(4-chlorobenzoyloxy)-4'-(4-methyl benzoyloxy)-azobenzene; -3-Cl : 2-(3-chlorobenzyloxy)-3-n-hexyloxy-4-(4-chlorobenzoyloxy)-4'-(4-methyl benzoyloxy)-azobenzene.The originality of these three compounds is essentially due to the presence of a substituted benzyloxy group, more voluminous, which is close to the n-hexyloxy flexible chain. Retention properties of these new liquid crystals have been characterised by the capillary column treated and impregnated according to the dynamic method. The position, ortho or para, of the methyl group on benzyloxy does not interfere significantly on the retention mechanism. In the case of the replacement of the methyl group by a halogen atom (chlorine), we noticed a radical change of the retention properties. To cite this article: D. Belaïdi et al., C. R. Chimie 5 (2002) 591-598 © 2002 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS gas chromatography / stationary phases / liquid crystals Résumé -Les performances analytiques de trois phases stationnaires « cristal liquide » à chaîne latérale sont présentées. Les composés mésogènes étudiés dans ce travail sont : -3-CH 3 : 2-(3-méthylbenzyloxy)-3-n-hexyloxy-4-(4-chlorobenzoyloxy)-4'-(4-méthyl benzoyloxy)-azobenzene ; -4-CH 3 : 2-(4-méthylbenzyloxy)-3-n-hexyloxy-4-(4-chlorobenzoyloxy)-4'-(4-méthyl benzoyloxy)-azobenzene ; -3-Cl : 2-(3-chlorobenzyloxy)-3-n-hexyloxy-4-(4-chlorobenzoyloxy)-4'-(4-méthyl benzoyloxy)-azobenzene. L'originalité de ces trois composés réside essentiellement dans la présence du substituant benzyloxy, plus volumineux, à proximité de la chaîne flexible n-hexyloxy. Les propriétés de rétention de ces nouveaux composés cristaux liquides ont été mises en évidence grâce à l'utilisation de colonnes capillaires traitées et remplies selon la méthode dynamique. Le passage du radical méthyle porté par le substituant latéral benzyloxy de la position méta vers la position para ne modifie pas d'une manière importante le mécanisme de rétention. En revanche, une meilleure aptitude à séparer certains composés chimiques doués de volatilité et de polarité différentes est obtenue avec la phase 3-Cl lorsque le radical méthyle est remplacé par le chlore. Pour citer cet article : D. Belaïdi et al., C. R. Chimie 5 (2002) 591-598 © 2002 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS chromatographie en phase gazeuse / phases stationnaires / cristaux liquides * Correspondance et tirés à part.
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