PRESSURE-DROP EFFECTS ON SELECTIVITY AND RESOLUTION IN PACKED-COLUMN SUPERCRITICAL-FLUID CHROMATOGRAPHY

The influence of pressure drop on retention, selectivity, plate height and resolution was investigated systematically in packed supercritica l fluid chromatography (SFC) using pure carbon dioxide as the mobile p hase, Numerical methods developed previously which enabled the predict ion of pressure gradients, diffusivities, capacity factors, plate heig hts and resolutions along the length of the column were used for the m odel calculations, The effects of inlet pressure and supercritical flu id flow rate on selectivity and resolution are studied, In packed colu mn SFC with pure carbon dioxide as the mobile phase, the pressure drop can have a significant effect on resolution, The flow rate is shown t o have a larger effect than generally realized, The calculated data ar e shown to be in good agreement with the experimental results, Finally , the variation of the chromatographic parameters along a 5.5 meter lo ng model SFC column is illustrated, The possibilities and limitations of using long packed columns in SFC are discussed, It is demonstrated that long columns with large plate numbers do not necessarily yield be tter separations.