Determination of optical purity by nonenantioselective LC using CD detection

The use of a circular dichroism (CD) based HPLC detection system was recently described by some authors and proposed for a nonenantioselective HPLC enantiomeric purity determination. Indeed the system, measuring both CD and UV signals simultaneously, allows the evaluation of the g anisotropy factor. In order to experimentally support such an analytical procedure as an alternative to the enantioselective chromatographic method currently found in some pharmacopoeial monographs, we have studied its application to the analysis of dexchlorpheniramine maleate, an active substance which exhibits a poor CD signal in the 250-270 nm spectral region with a g value of the order of 10(-4). The results reported indicate that the suitability of the studied procedure for the enantiomeric purity determination is obtained only when the CD-detector reaches high stability; indeed a certain time lag is systematically necessary to obtain stable responses, i.e. adequate precision. The enantioselective HPLC procedure seems to be more precise for enantiomeric purity values < or = 2% than the CD based detection system; such a disadvantage might be counterbalanced by the use of non chiral stationary phases.