Effect of acidic mobile phase additives on chiral selectivity for phenylalanine analogs using subcritical fluid chromatography

A variety of acidic mobile phase additives were investigated as to their ef fects on retention, selectivity, efficiency, and overall chiral resolution for a number of chiral N-substituted phenylalanine analogs under subcritica l conditions. These mobile phase additives showed significant effects for a ll of the chromatographic parameters evaluated in this study. All of the ph enylalanine analogs showed decreasing retention as the pK(a) of the additiv e decreased. Plots of selectivity, efficiency, and chiral resolution showed pronounced improvement using acidic additives with pK(a) values near -1. T hese results demonstrated that the choice of acidic mobile phase additives had a significant effect on the resulting chromatography for these chiral a nalytes under subcritical conditions. (C) 1999 Wiley-Liss, Inc.