Separation of Isomers on Nematic Liquid Crystal Stationary Phases in Gas Chromatography: A Review

Understanding the composition of complex hydrocarbon mixtures is important for environmental studies in diverse fields, but many prevalent compounds cannot be confidently identified using traditional gas chromatography (GC) techniques. Increasing requirements on analyses of isomeric compounds and the problems encountered in their separation demand a study of more efficient systems which exhibit a high selectivity. Kelker and Fresenius first used nematic liquid crystals as stereospecific stationary phases in GC. Nematic liquid crystal has shown this particular selectivity and sensitivity as stationary phases for the separation of isomers having similar volatilities. Because of their unique selectivity towards rigid solute isomers, liquid crystal stationary phases were considered at one time to be a very promising class of materials that give gas chromatographic separations very different from those that can be obtained with any other stationary phase. Since then, a great deal of attention has been paid to the separation properties of this relatively wide group of substances. Liquid crystal can be used to separate a variety of compounds including isomer mixtures which cannot be separated on conventional stationary phases. This paper aims to review all specific experimental results and presents a comparative analytical study of monomeric nematic liquid crystal stationary phases used in GC. A further contribution of this review is in the field of isomeric compounds separation.