DETERMINATION OF ENANTIOMERIC EXCESS USING RAMAN OPTICAL-ACTIVITY

A simple method for the determination of enantiomeric excess is described. It is based on depolarized Raman optical activity (ROA) measurements in right-angle scattering employing the incident circular polarization (ICP) modulation approach. The accuracy of this method was assessed utilizing alpha-pinene as a chiral test compound The four alpha-pinene ICP ROA signals associated with the Raman bands observed at ca. 772, 787, 887 and 929 cm(-1) were selected to establish a linear relationship between ROA signal strength and enantiomeric composition for a set of calibration mixtures containing both alpha-pinene enantiomers. Using this relationship, a (+)-alpha-pinene sample content of 163% was determined for a blind mixture containing 83.6% (1S)-(-)-alpha-pinene and 16.4% (1R)-(+)-alpha-pinene, Similarly, utilizing additional spectral subtraction procedures, a (+)-alpha-pinene sample content of 1.5% was estimated for a test mixture consisting of 50.1% (1S)-(-)alpha-pinene and 49.9% (1S)-(-)-trans-pinane.