ASSESSMENT OF THE POLARITY OF 3 LIQUID-CRYSTALS USED AS GAS-CHROMATOGRAPHIC STATIONARY PHASES

Attempts to evaluate the polarity of three liquid crystals used in packed gas chromatographic columns suggest that more than one method is required at different temperatures. At 120-degrees-C a triangular proportional plot of retention indices using three McReynolds' solute probes indicate azoxydiphenetole (ADP) and bis(methoxy-benzylidineanilchloroaniline) [(MBCA)2] are reasonably strong in polarity. Bis(methoxybenzylidineanilbitoluidine) [(MBT)2] is moderately polar, compared to normal-phase columns. At 160-degrees-C, however, using the sum of retention indices of three C-10 volatile oil constituents, ADP and (MBCA), rate as only moderately polar, with (MBT)2 now exhibiting low polarity. The polarity sequence of the three liquid crystals (unmelted, melted and supercooled) is confirmed by the second method. Their polarity rating is method-sensitive, although they change in polarity more than normal chromatographic phases with temperature alterations. The selection of a liquid crystal for particular separations is discussed.