In this study, the peak capacities for packed capillaries used in various forms of chromatography were investigated. Experiments found that the peak width at halfheight (w 1/2 ) linearly increased with increasing retention time when operating under isothermal, isobaric, and isocratic conditions in capillary gas chromatography, solvating gas chromatography, supercritical fluid chromatography, and liquid chromatography. From this relationship, a general peak capacity (n) expression was obtained. This expression covers conventional packed, packed capillary, and open tubular column chromatographies. With this general expression, it is possible to directly compare the separating capabilities of the various column types and chromatographic techniques.

In this study, organic solvents at temperatures higher than their normal boiling points were used as mobile phases for packed capillary column chromatography. No restrictor or back pressure was imposed on the column outlet. As a result, a large difference in mobile-phase properties existed, and a phase transformation from liquid to gas occurred, along the column. Solvating gas chromatography (SGC) was used to characterize this chromatographic process because, near the column outlet, a gaseous mobile phase existed. Chromatographic performance characteristics including mobile-phase flow, column efficiency, mobile-phase solvating power, and solute retention were investigated using fused-silica capillary columns packed with microparticles (5-and 10-µm diameters). It was found that when the temperature was increased to values that were higher than the normal mobile-phase boiling point, the mobile-phase linear velocity increased rapidly at constant column inlet pressure. Although large differences in mobile-phase properties existed between the column inlet and outlet, high column efficiencies (reduced plate heights of less than 2) were achieved. At elevated temperature, the optimum mobile-phase linear velocity increased, and the dependence of column efficiency on linear velocity decreased. Solute retention factors also decreased with increasing temperature, even for temperatures higher than the normal boiling point of the mobile phase. Large polycyclic aromatic hydrocarbons and enantiomers were rapidly separated under SGC conditions.