APPLICATIONS OF A SENSITIVE LASER POLARIMETRIC HPLC DETECTOR: CONFIRMATION OF ENANTIOMERIC EXCESS FOR DANOFLOXACIN AND ANALYSIS OF A NOVEL MACROLIDE

Abstract

A commercially available laser-based polarimetric detector (Chiral Detector) was used to confirm the enantiomeric excess of danofloxacin and to analyze a novel macrolide. The detector is based on the work of Yeung et al.[1] and uses a low noise laser diode which emits 675 nm radiation. Selectivity is obtained not through chromatographic resolution but through the sign and magnitude of detector response. An area ratio of the detector signals (Chiral/UV) was used to calculate Danofloxacin's optical purity. By calculating the ratio of the two detector signals an accurate measure of optical purity or enantiomeric excess can be calculated relative to standard responses without concern for potency, optical rotation of impurities, exact sample concentration or injection precision. The molecule is ideal for this type of determination since it absorbs UV radiation strongly, has a large optical rotation and the HPLC method resolves potential process impurities, synthetic byproducts and degradation products. The signal ratio was found to be linear with respect to % optical purity from 100% to 0% and is expected to be accurate to within 2%. Samples of danofloxacin mesylate were optically pure to within the 2% limit of the methodology. A novel experimental macrolide was analyzed using a reversed phase HPLC system interfaced to both a UV detector and a laser-based polarimetric detector. Specific rotation of the novel macrolide was determined to be −23° in mobile phase using a bench top polarimeter. While polarimetric response for the experimental macrolide was shown to be reasonably linear from 0.1mg/mL to 1.5mg/mL, sensitivity was poor relative to UV detection at 210nm. The limit of quantitation was ∼5000 ng for the laser-based polarimetric detector which was 50 times less sensitive than the UV detector.