Synthesis and Characterization of a Liquid Crystal Containing Oxadiazole and Its Performance for the Separation of Isomers by Gas Chromatography

Liquid Crystals as Stationary Phases in Chromatography

“…Benalia et al [ 30 – 33 ] have described in detail the influence of the chemical structure of three nematic LCs on their separation properties towards about eighty analytes belonging to the different groups of chemical compounds. These LCs have the same basic structure with different substituents, namely: 5-[4-(4-methoxyphenylazo)phenyl]-2-butylthio-1,3,4-oxadiazole—Phase I, 5-[4-(4-butyryloxyphenylazo)phenyl]-2-butylthio-1,3,4-oxadiazole—Phase II, and 5-[4-(4-propoxyphenylazo)phenyl]-2-butylthio-1,3,4-oxadiazole—Phase III (see “ Appendix: The Characteristics of Liquid Crystals Investigated as Stationary Phases ”).…”

“…As expected, the retention times increased with the number of methyl substituents, as for xylene, trimethylbenzene, tetramethylbenzene, and hexamethylbenzene, so in the same order than their respective boiling points. This apart, it could be noticed that 1,2,3-trimethylbenzene was more retained than 1,2,4-trimethylbenzene, and the following order was observed: t -butylbenzene > i -butylbenzene > diethylbenzene > tetramethylbenzene in the three phases [ 30 – 33 ]. The main factor in determining their retention is the symmetry of substitution.…”

“…The main factor in determining their retention is the symmetry of substitution. Benelia et al observed the 1-methylnaphtalene and 2-methylnaphtalene elution order in the III phase and the inverse order in the I and II phases [ 30 – 33 ]. The observed elution order for dimethylnaphtalenes in the three phases was the same, namely, 2,6-dimethylnaphtalene < 1,6-dimethylnaphtalene < 1,5-dimethylnaphtalene < 2,3-dimethylnaphtalene.…”

“…The authors explained such behaviour by the strong interactions between two phenyl rings with the hydroxyl substituent in an ortho -position, which distorted the molecule from the planar shape. The retention time lengthened as the number of methyl groups attached to molecules of xylene, trimethylbenzene, tetramethylbenzene, and hexamethylbenzene were in accordance with the increasing values of their boiling temperatures [ 32 , 33 ]. In this case, the difference in chemical structure of the molecules has no essential influence on the separation effects of the components of the same mixtures [ 30 ].…”