SHAPE SELECTIVITY ASSESSMENT OF STATIONARY PHASES IN GAS-CHROMATOGRAPHY

Column selectivity is examined for a series of smectic liquid crystall ine columns and is compared with methyl and C18 polysiloxane columns f or the separation of polycyclic aromatic hydrocarbon (PAH) isomers. A set of e,tended and condensed solute probes is described that provides a sensitive indication of variations in column shape selectivity. Exa mples of shape selectivity differences are presented for smectic liqui d crystalline columns and 5% phenyl polysiloxane columns using various PAH isomer sets. Variations in selectivity have been observed among d ifferent smectic liquid crystalline columns, and this problem appears more significant than for methyl polysiloxane columns. The selectivity ratio for tetraphenylmethane and p-terphenyl provides a sensitive ind ication of column shape selectivity, with a change in elution order oc curring between ordered (smectic liquid crystalline) columns and non-o rdered (methyl polysiloxane) columns. Shape selectivity differences in dicated by this test mixture are apparent for more complex PAH isomer mixtures. Despite stationary phase selectivity variability, smectic li quid crystalline columns offer considerable potential for solving diff icult separation problems involving structured solutes.