RETENTION IN COUPLED CAPILLARY COLUMN SUPERCRITICAL-FLUID CHROMATOGRAPHY WITH LIPIDS AS MODEL COMPOUNDS

We have investigated to which extent retention data, acquired on singl e capillary columns, can be used for predicting retention factors in a coupled column system. For this purpose we utilized a model mixture o f 18 lipid components with widely different vapor pressures and polari ties. The sample was chromatographed on two columns, SB-biphenyl-30 (7 0% methyl-30% biphenylpolysiloxane) and SB-cyanopropyl-50 (50% methyl- 50% cyanopropylsiloxane). Experimental retention factors, acquired in coupled column systems with two columns connected in different order, were thus compared with values calculated from runs on each single col umn. The agreement between calculated and experimental values generall y was better than 5% without any pressure drop correction. To study th e possibility of predicting retention behavior in a wide pressure rang e from a limited number of experiments, we also investigated the relat ion between solute retention and mobile phase density. We found that a ll data could be fitted to second order equations, which gives the pos sibility to optimize the resolution with respect to pressure from a li mited number of runs at different pressures.