Gas-liquid chromatography of polychlorinated biphenyl congeners between a nematic liquid crystal phase and a nonpolar phase

Abstract

The gas-liquid chromatographic retention behavior of 54 polychlorinated biphenyl (PCB) congeners containing one to ten chlorine atoms was evaluated on a nematic liquid crystal (N,N'-bis(p-methoxybenzylidene)-..cap alpha..,..cap alpha..'-bi-p-toluidine, BMBT). To a first approximation, as anticipated, retention on the liquid crystal appeared to be enhanced with an increasing molecular length-to-breadth ratio for congeners containing the same number of chlorine atoms. The retention behavior of 38 of the PCB's also was examined on a nonselective, nonpolar stationary phase (Apolane-87) in which retention is controlled more by solute vapor pressure differences than by solute-stationary phase free energy effects. The difference in the free energy of mixing of PCB solute pairs between the two phases was found to be predominantly greater in the liquid crystal phase, demonstrating an enhanced selectivity for PCB isomer separations over nonpolar phases. The retention data suggest that the separation of many of the congeners might be improved by using a liquid crystal stationary phase.