EFFICIENCY IN PACKED-COLUMN SUPERCRITICAL FLUID CHROMATOGRAPHY USING A MODIFIED MOBILE PHASE

Large density differentials across small particle packed columns failed to produce losses in chromatographic efficiency. The mobile phase consisted of carbon dioxide modified with methanol. The largest density differential across the column involved an outlet density below 0.2 g/cm3 while the density at the inlet was simultaneously above 0.9 g/cm3. Absolute efficiencies were similar to those found using the same particle size in reversed-phase liquid chromatography and were very near theoretically predicted values. In related experiments, two cases were found where low outlet pressures or densities caused degraded peak shapes. Experimental conditions were compared to vapor-liquid equilibria data. Poor peak shapes were likely caused by the mobile phase separating into two phases and/or solubility problems.