Competition between the (+)-and (-) enantiomers of 2,2,2-tritluoro-1-(9-anthryl) ethanol as mobile phase additives was indicated by the chromatographic behavior of their system peaks. Two types of chiral stationary phases were used, one based on dinitrobenzoylphenylglycine and the other on dinitrobenzylphenylethylamine plus tartaric acid.The racemic mixture was used as the mobile phase additive and K' of their system peaks was studied as a function of the mixture concentration in the mobile phase in both cases. A shift in K' of the two system peaks was observed and considered as an indication that competition occurred. The areas of the two system peaks were also studied as a function of the concentration of the enantiomers in the samples, using two different compositions of the mobile phase. The dependency of system peaks' area on the sample composition indicated whether competition between the enantiomers occurred. One mobile phase contained 0.1 mM of the racemic mixture, where the area of the two retained system peaks behaved independently, i.e., only the peak corresponding to the enantiomer was affected by its presence in the sample. The other mobile phase contained 0.75 mM of the racemic mixture, and both peaks were affected by the injection of any one of the enantiomers. The interdependency of the system peaks' area on both the enantiomers indicated that their distribution in the chiral system was interrelated due to mutual interactions. A quantitative treatment of the interdependency and competition was excluded, due to the irreversible adsorption of the two enantiomers on the chiral stationary phase after using overloading concentrations. This irreversible adsorption was visualized by the appearance of two retained system peaks of the two residual enantiomers. These system peaks were detected only when the sample contained pure enantiomers due to competition between the enantiomer in the sample with the residual enantiomers in the stationary phase.o 1994 Wiey-Liss, Inc.KEY WORDS: chiral stationary phase, dinitrobenzylphenylethylamine, dinitrobenzoylphenylglycine, enantiomers, 2,2,2-trifluoro-l-(9-anthryl) ethanol, competition, nonlinear, liquid chromatography, system peaks The drive for chiral separations using liquid chromatography, either analytical or preparative, has intensified in recent years especially due to the growth in pharmaceutical applications.14 When preparing chiral compounds by asymmetric synthesis there is always a possibility that the product will be accompanied by residues of the unwanted enantiomer. In many cases an absolutely pure enantiomer can be obtained only after its purification by chromatographic separation. An intriguing mode of chromatography is the self-induced separation in achiral chromatography. 7-12 In these cases nonracemic mixtures of enantiomers are used, and the enantiomer in excess functions as a chiral solvating agent. Therefore, when introduced into achiral systems, the mutual diastereomeric interactions cause a self-induced separation into the racemate an...
