Analysis of enantiomers giving partially overlapped peaks by using different treatments of the chromatographic ultraviolet signals: quantification ofpseudoephedrine enantiomers

Different strategies for the quantification of partially coeluting optical isomers have been investigated. The methods tested are based on the use of different features as the analytical UV signals: peak heights, perpendicula r drop areas, first and second derivatives of the chromatograms, peak areas obtained by deconvolution of the overlapped peaks with data fitting optimi zation, and a multivariate model (principal component regression, PCR). The amphetamine-derivative drug pseudoephedrine was selected as a model compou nd. For chromatography, LiChrospher 100 RP18 and a mobile-phase consisting of methanol and a solution of carboxymethyl-beta -cyclodextrin (the chiral selector) were used. The UV detector was set at 215 mn. The accuracy obtain ed with the tested methods at different degrees of overlapping and at diffe rent concentration ratios between enantiomers was evaluated. The results of this study demonstrated that the best option for quantification of partial ly overlapped UV peaks of enantiomers and to obtain the enatiomeric excess is the use of a PCR model using peak heights, perpendicular drop peak areas and deconvoluted peak areas as the original variables. The predictive abil ity of the proposed calibration model is of about 2-8 times better (dependi ng on the overlapping degree) than that achieved with the other models test ed. (C) 2001 Elsevier Science B.V. All rights reserved.