SOLVENT SELECTIVITY IN CHIRAL CHROMATOGRAPHY USING A BETA-CYCLODEXTRIN-BONDED PHASE

A beta-cyclodextrin-bonded phase has been used to investigate the sepa ration of the enantiomers of atenolol, oxprenolol, celiprolol, tertato lol, terbutaline, fluoxetine, norfluoxetine, and zopiclone, focusing o n the importance of solvent selectivity. With cyclodextrin (CD)-bonded phases, chiral discrimination occurs because the two enantiomers of a racemate form inclusion complexes of different strengths within the C D cavity. The organic modifier molecules tend to compete with solutes for a definite number of adsorption sites on the stationary phase. Mor eover, the ternary complex formation may play an important role in chi ral recognition. In this study, it was of interest to estimate the inf luence of mobile phase modifiers with respect to solvent type (i.e., A CN, MeOH, EtOH, THF, i-PrOH, PrOH and t-BuOH), size and shape, and con centration. Solvent selectivity has been investigated by using differe nt organic modifiers in mobile phases with the same polarity, and rela tionships were established between the logarithm of solvent partition coefficient (log P-s) and the three most important chromatographic par ameters: retention time (t), resolution (R), and enantioselectivity (a lpha). Thus, it seems that the hydrophobicity of the organic modifier becomes one of the dominant factors affecting the inclusion process ph enomena. Further, the apparent partition coefficients of the compounds under study have been determined and a comparison has been attempted regarding the degree of their enantiomeric resolution. (C) 1995 Wiley- Liss, Inc.