COMPARISON OF STATIONARY PHASES FOR PACKED-COLUMN SUPERCRITICAL FLUID CHROMATOGRAPHY

A study of the applicability of different stationary phases for packed-column supercritical fluid chromatography is described. The compatibility of these phases with carbon dioxide and with a number of test solutes was established qualitatively from the observed peak shapes. Retention and selectivity differences between the different columns were studied quantitatively. The stationary phases studied include chemically modified silicas, polysiloxane-coated silicas, modified and unmodified porous graphitic carbon and modified and unmodified poly(styrene-divinylbenzene) copolymers. It is concluded that differences in selectivity between different stationary phases are often due to interactions between the solute molecules and active sites on the surface. Such interactions lead to poor peak shapes and are therefore undesirable. For most of the solutes studied, with the notable exception of polyaromatics, a poly (ethylene glycol)-coated carbon phase provided the best results. Owing to the very high retentivity of unmodified carbon, this phase turned out to be very stable. The coating of different types of polymers on solid surfaces may be used to create stationary phases without residual active adsorption sites, but with considerable differences in selectivity. © 1990.