Effects of pressure drop, particle size and thermal conditions on retention and efficiency in supercritical fluid chromatography.
The effects of particle size and thermal insulation on retention and efficiency in packed-column supercritical fluid chromatography with large pressure drops are described for the separation of a series of model n-alkane solutes. The columns were 2.0mm i.d.x150mm long and were packed with 3, 5, or 10-mum porous octylsilica particles. Separations were performed with pure carbon dioxide at 50 degrees C at average mobile phase densities of 0.47g/mL (107bar) and 0.70g/mL (151bar). The three principal causes of band broadening were the normal dispersion processes described by the van Deemter equation, changes in the retention factor due to the axial density gradient, and radial temperature gradients associated with expansion of the mobile phase. At the lower density the use of thermal insulation resulted in significant improvements in efficiency and decreased retention times at large pressure drops. The effects are attributed to the elimination of radial temperature gradients and the concurrent enhancement of the axial temperature gradient. Thermal insulation had no significant effect on chromatographic performance at the higher density. A simple expression to predict the onset of excess efficiency loss due to the radial temperature gradient is proposed.
Poe
Donald P
DP
Department of Chemistry and Biochemistry, University of Minnesota Duluth, 10 University Drive, Duluth, MN 55812, USA. dpoe@d.umn.edu
Schroden
Jonathan J
JJ
D025924:Chromatography, Supercritical Fluid / Q000295:instrumentation* / Q000379:methods; D010316:Particle Size; D011312:Pressure; D012117:Resins, Synthetic / Q000737:chemistry*; D013696:Temperature
D012117:Resins, Synthetic