Determination of enantiomeric excess using the ultraviolet-circular dichroism and the high-performance liquid chromatography-circular dichroism methods.
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.
Chen
Li
L
Chemical & Process Engineering Centre, 4 Engineering Drive 4, Block E5, Singapore 117576.
Zhao
Yanjun
Y
Gao
Feng
F
Garland
Marc
M
D000465:Algorithms; D002851:Chromatography, High Pressure Liquid; D002930:Cinchona Alkaloids / Q000737:chemistry; D002942:Circular Dichroism / Q000379:methods*; D045424:Complex Mixtures / Q000032:analysis*; D000431:Ethanol / Q000737:chemistry; D007773:Lactates / Q000737:chemistry; D012015:Reference Standards; D015203:Reproducibility of Results; D013237:Stereoisomerism; D014466:Ultraviolet Rays
D002930:Cinchona Alkaloids; D045424:Complex Mixtures; D007773:Lactates; C041622:cinchonidine; D000431:Ethanol; C015866:ethyl lactate