Modelling of retention in analytical supercritical fluid chromatography for CO2-Methanol mobile phase

Mathematical modelling of the chromatography process requires knowledge of the isotherm model. Therefore a necessary step in calculations is estimation of the isotherm model parameters. In this study the inverse method has been successfully used to estimate the linear isotherm model parameters in supercritical fluid chromatography (SFC). Estimation was based on measured retention times of experimental band profiles. The solute was n-octadecylbenzene. The mobile phase was carbon dioxide-methanol, 95/5% (v/v), and the column was 250 mm × 4.6 mm i.d. packed with 5-micron Luna C18(2) particles. The experiments were done for outlet pressures from 100 bar to 150 bar at different flow rates and different sets of experimental conditions: (1) column operated under convective air (CA); (2) column operated in still air conditions. Moreover in the latter thermal mode were considered two cases. In the first case the temperature of the oven air was different from the inlet temperature of the mobile phase. In the second case the temperature of the oven air was the same as inlet temperature of the mobile phase. The column efficiency was also analysed.