Gas chromatographic properties of mixed liquid crystal stationary phases

Abstract

The gas chromatographic properties of six stationary phases containing various mixtures of the liquid crystals N,N′-bis( p-methoxybenzylidene)-α,α′-bi- p-toluidine and N,N-bis( p-ethoxybenzylidene)-α,α′-bi- p-toluidine are reported in both their supercooled and normal nematic temperature ranges. At temperatures at which all mixtures are in their nematic states, separations of 1,3- and 2,3-dimethyl-naphthalene, and anthracene and phenanthrene are highest for the stationary phases containing the highest percentage of N,N′-bis( p-ethoxybenzylidine)-α,α′-bi- p-toluidine. Since the mixed stationary phases can operate at lower temperatures than the pure compounds, it is possible to obtain better separations. Additionally, the liquid crystals interact with the support material, causing the crystal-to-nematic transition temperatures of the mixed-phase column packings to be generally lower than those of the liquid crystal mixtures themselves. This interaction also changes the eutectic composition of the mixed-phase packings. The results demonstrate that the use of mixed stationary phases improves selectivity and extends the usable temperature range of liquid crystal gas chromatographic columns.