Determination of enantiomeric purity by simultaneous dual circular dichroism and ultraviolet spectroscopy.
A method is described for the determination of enantiomeric composition. The ellipticity and absorbance of the sample are measured simultaneously by CD and UV spectroscopies, and the resulting G value is determined. G is an intensive physico-chemical parameter, a close derivative of anisotropy factor. Its magnitude is identical with opposite sign for enantiomers. The experimental G value is concentration-independent, as long as both absorption and ellipticity are linear functions of concentration. 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 chromatographic purification. By virtue, the method lacks several sources of error, arising normally from concentration inaccuracies. Applicability of the principles is tested by the example of phenylglycine and mandelic acid. Advantages of the method allowed the determination of phenylglycine enantiomer purity with an accuracy of 0.1%.
Horváth
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P
Semmelweis University, Institute of Pharmaceutical Chemistry, Hôgyes Endre u. 9. Budapest H-1092, Hungary.
Gergely
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A
Noszál
B
B