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 effects on retention, selectivity, efficiency, and overall chiral resolution for a number of chiral N-substituted phenylalanine analogs under subcritical conditions. These mobile phase additives showed significant effects for all of the chromatographic parameters evaluated in this study. All of the phenylalanine analogs showed decreasing retention as the pKa of the additive decreased. Plots of selectivity, efficiency, and chiral resolution showed pronounced improvement using acidic additives with pKa values near −1. These results demonstrated that the choice of acidic mobile phase additives had a significant effect on the resulting chromatography for these chiral analytes under subcritical conditions. Chirality 11:91–97, 1999.