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Determination of Enantiomeric Excess using the Ultraviolet-Circular Dichroism and the High-Performance Liquid Chromatography-Circular Dichroism Methods
Volume 57, Number 7 (July 2003) Page 797-804
Chen, Li; Zhao, Yanjun; Gao, Feng; Garland, Marc
Two useful numerical methods using ultraviolet (UV) and circular dichroism (CD) spectroscopies are proposed to determine enantiomeric excess (e.e). An algorithm is also proposed to generate self-consistent pure R and S enantiomer reference spectra. After all pure reference spectra are generated, a simulated annealing algorithm is applied to minimize the mismatch between the experimental spectra and the spectra after a least-squares fit. Optimal factors for R and S enantiomers are then used to determine e.e. The ultraviolet-circular dichroism (UV-CD) method uses the combined UV and CD spectra in a composite form, while the high-performance liquid chromatography (HPLC)-CD method only employs the CD spectra with the total concentrations of R plus S enantiomers provided by HPLC using a non-chiral stationary phase. Both methods were successfully tested on mixtures with known composition and then applied to real experimental data (unknown compositions). Compared with the UV-CD method, the results show that excellent results are more readily obtained using the HPLC-CD method. With the systems studied, the latter usually provided outstanding estimations of e.e with low error percentages.