Effect of pore size on speed of chiral separations using packed capillary column SFC

beta -Cyclodextrin polysiloxane-encapsulated 10-mum silica particles with p ore sizes of 80, 300, and 1400 Angstrom were prepared for evaluation in pac ked capillary column supercritical fluid chromatography with neat carbon di oxide as the mobile phase. The effects of pore size on linear velocity, ret ention, selectivity, efficiency, resolution, and resolution per unit time w ere investigated. It was found that at constant pressure, the highest linea r velocity was obtained for columns containing particles of 80 A pores, fol lowed by particles with 1400 Angstrom and then 300 Angstrom pores. The high est column efficiency was achieved using 1400 A pore particles, indicating that convective mass transfer was generated by a very small portion of mobi le phase flowing through the larger pores. The chiral selectivity generally increased as the pore size increased. There was no significant difference between 80 and 1400 Angstrom pore particles in terms of resolution per unit time. Both can be used to achieve rapid separations of small enantiomers, such as (+/-)-1-phenylalcohol in 3 min. (C) 2000 John Wiley & Sons, Inc.