Chiral packed column subcritical fluid chromatography on polysaccharide and macrocyclic antibiotic chiral stationary phases.

The polysaccharide chiral stationary phases (CSPs) Chiralcel OD and Chiralpak AD, and the macrocyclic antibiotic CSPs Chirobiotic V and Chirobiotic T were evaluated in packed column subcritical fluid chromatography (pSFC) for the separation of different types of racemic compounds (beta-blockers, beta-agonists, benzodiazipines, non-steroidal anti-inflammatory drugs, barbiturates, free and derivatized amino acids, etc.). The same conditions and program could be applied to check the applicability and enantioselectivity of one of the CSPs for a given racemic mixture. The conditions are: temperature 30 degrees C, pressure 200 bar, flow-rate 2 ml/min, carbon dioxide, modifier methanol containing 0.1% trifluoroacetic acid (TFAA) and 0.1% triethylamine (TEA) with a gradient from 5% (5 min) to 30% at 5%/min. A resolution of 0.4 under those conditions generally indicates that baseline separation can be realized on the CSP by fine-tuning the different parameters of the SFC separation. The best CSP for pSFC proved to be Chiralpak AD which provided separation for 70% of the 44 substances tested, followed by Chiralcel OD (66%), Chirobiotic T (50%) and Chirobiotic V (48%). For comparison, the enantioselectivity in pSFC of the brush type CSPs Chirex 3022 with pi-donor characteristics and Chirex 3005 with pi-acceptor characteristics was also evaluated. As expected, these phases perform poorly under SFC conditions, on Chirex 3022 (34%) and on Chirex 3005 (20%). (C) 1997 Elsevier Science B.V.