Effect of pressure drop on solute retention and column efficiency in supercritical fluid chromatography

The effect of pressure drop on the performance of supercritical fluid chromatographic systems is studied. Experiments have been conducted at different pressures and at 55 and 65 degrees C. Experiments at conditions leading to large and small pressure drops have been performed. Parameters to describe the pressure drop, retention time and efficiency have been extracted from these experiments. Using these parameters the dynamics of the chromatographic column have been modeled. Darcy's law was used to describe the pressure drop. The efficiency was modeled by considering the contributions from axial dispersion, resistance to mass transfer from the fluid film, and to diffusion in the pores. Good description of the pressure drop, retention time and mass transfer characteristics under normal operating conditions was obtained. The parameters extracted were used to predict the elution profile by numerical simulations. Considerable loss in column efficiency was observed when operating the column at lower values of the back pressure.