THERMODYNAMIC STUDY OF SOLUTE RETENTION ON A SMECTIC LIQUID-CRYSTALLINE PHASE IN SUPERCRITICAL FLUID CHROMATOGRAPHY

Capillary supercritical fluid chromatography was used to obtain the values for entropy and enthalpy of solute transfer as a function of density for isomeric polycyclics on a smectic liquid-crystalline stationary phase. The values were compared with those obtained from a structurally similar nonmesomorphic stationary phase. Two different fluids were investigated, and it was determined that carbon dioxide has a greater affinity for both stationary phases, than does nitrous oxide. Retention behavior in the vicinity of the glassy-to-smectic transition was also investigated and found to depend on the mobile-phase density but not on the mobile-phase polarity. The appearance of a plateau at certain densities is explained by a pretransition region. © 1990 American Chemical Society.