DEVELOPMENT OF A BIMODAL POLARIMETRIC RESPONSE MODEL FOR IMPROVED QUANTITATION OF ENANTIOMERIC MIXTURES UNDER CONDITIONS OF POOR CHROMATOGRAPHIC RESOLUTION

The combination of a chiral-selective separation mode with polarimetri c detection was investigated in terms of its ability to quantitate ena ntiomeric mixtures of the dansylated derivatives of phenylalanine, thr eonine, and valine under conditions of poor chromatographic resolution . Using the difference between two Gaussian functions to model the bim odal response obtained using polarimetric detection and incomplete chi ral resolution, correlation coefficients as high as 0.999 were obtaine d when actual enantiomeric fractions were plotted against observed ena ntiomeric fractions calculated from the fitting procedure. The methodo logy was evaluated at different levels of chromatographic resolution, and as a function of the sign and magnitude of the specific rotation o f the model compounds. Limits of quantitation calculated at different levels of enantiomeric excess demonstrate the potential of the method to quantitate enantiomeric mixtures even under conditions of poor chro matographic resolution. Minimum measurable quantities (MMQ) at, or bel ow the 1.0% enantiomeric excess tee) level were obtained for the three amino acid derivatives tested under various conditions of chromatogra phic resolution when the polarimetric data were fit to the bimodal res ponse model. Even under the lowest resolution conditions tested, the M MQ was determined to be at the 5% ee level. (C) 1998 Elsevier Science B.V. All rights reserved.