The Influence of Temperature, Ultrasonication and Chiral Mobile Phase Additives on Chiral Separation; Predominant Influence of β-Cyclodextrin Chiral Mobile Phase Additive Under Ultrasonic Irradiation

This paper introduces a technique for resolving amino acids that combines the advantages of the conventional CSP (chiral stationary phase) method with the CMPA (chiral mobile phase additive) method. A commercially available chiral crown ether column, CROWNPAK CR(+), was used as the CSP and three cyclodextrins (beta-CD, gamma-CD, HP-beta-CD) were used as the mobile phase additives. Chromatographic resolution was performed at 25 degrees C and 50 degrees C with or without sonication. A comparison of the chromatographic results under ultrasonic conditions with those under non-ultrasonic conditions showed that ultrasound decreased the elution time and enantioselectivity at all temperatures. In the case of the beta-CD mobile phase additive, the elution time and enantioselectivity under ultrasonic condition were significantly higher than under non-sonic condition at all temperatures. Commercially available Chiralpak AD, Whelk-O2 and Pirkle 1-J columns were used as CSPs to examine more meticulously the effects of ultrasonication and temperature on the optical resolution. The optical resolution of some chiral samples analyzed at 25 degrees C and 50 degrees C with or without sonication was compared. As in the previous case, the enantioselectivity was lower at 25 degrees C but similar enantioselectivity was observed at 50 degrees C.