DETERMINATION OF ENANTIOMERIC PURITY BY SIMULTANEOUS DUAL CIRCULAR-DICHROISM AND ULTRAVIOLET SPECTROSCOPY

A method is described for the determination of enantiomeric compositio n. The ellipticity and absorbance of the sample are measured simultane ously by CD and UV spectroscopies, and the resulting G value is determ ined. G is an intensive physico-chemical parameter, a close derivative of anisotropy factor. Its magnitude is identical with opposite sign f or enantiomers. The experimental G value is concentration-independent, as long as both absorption and ellipticity are linear functions of co ncentration. The analytical procedure introduced here is simple, rapid , and inexpensive, even though it includes calibration with standards of established enantiomeric composition. Provided the sample contains some UV-active contaminant(s), the method can be used after achiral ch romatographic purification. By virtue, the method lacks several source s of error, arising normally from concentration inaccuracies. Applicab ility of the principles is tested by the example of phenylglycine and mandelic acid. Advantages of the method allowed the determination of p henylglycine enantiomer purity with an accuracy of 0.1%. (C) 1997 Else vier Science B.V.