Comparison of two azobenzene liquid crystal stationary phases in open tubular column gas chromatography

Abstract

Comparative applications of two liquid crystals used as stationary phases in gas-liquid chromatography were investigated using different kinds of solutes. These liquid crystal molecules are: 4-(4-trans-pentylcyclohexanecarboxyloxy)-2′-methoxy-4′-(4-trans-pentylcyclohexanecarboxyloxy)-azobenzene (LC1) and 4-(4-trans-pentylcyclohexanecarboxyloxy)-2′-butoxy-3′-methyl-(4-butoxybenzoyloxy)-azobenzene (LC2). Their thermal properties were established with differential scanning calorimetry (DSC). The chromatographic separation abilities of LC1 and LC2 were studied using capillary glass columns. Interesting analytical performances were obtained in different fields: isomeric separation of alkanes, aromatics, polyaromatics, volatile aromatic compounds and cis- and trans-isomers. Comparison between LC1 and LC2 is presented. Elution properties of LC1 and LC2 showed some differences. LC2 exhibited a higher separation efficiency especially for alkanes, light aromatics and polyaromatics, and the elution orders of some solutes were reversed compared with LC1. Then, the two liquid crystals are efficient before and after solid-solid or solid-nematic transitions. Nevertheless, they present higher plate numbers in the nematic state. Nice separations of volatile aromatic compounds are obtained by the two liquid crystals.