Determination of enantiomeric purities using CD/CD detection

Enantiomeric purities are determined for binary mixtures of d-pseudoephedrine with the l-enantiomer and with the (+)- and (−)-ephedrines in bulk solutions using circular dichroism (CD) detection in the visible range. The molecules are individually derivatized by ligand exchange with tartrate in the first coordination sphere of Cu (II) metal complexes. Chiral-chiral interactions, after substitution, are specific enough to uniquely discrimmate among all four enantiomers using spectra for the mixed complexes. A univariate calibration model is used to predict enantiomeric purities for mixtures of the pseudoephedrines, and multivariate models are used for all three binary mixtures. Results for enantiomeric ratios that lie in the mole fraction range 0.95–1.00 are an improvement over current methods. Achiral mesotartrate is the optimum host ligand to use for the analysis of binary mixtures of diastereoisomers.