Resolution of (+)-cinchonine and (−)-cinchonidine by phase-modulation fluorescence spectroscopy

The different fluorescence lifetime profiles of the optical isomers (+)-cinchonine (CN) and (−)-cinchonidine (CD) have been used to resolve their mixtures, on the basis of phase and modulation fluorescence lifetime measurements. To resolve mixtures of these compounds two distinct approaches have been used: simultaneous equations from phase-resolved and modulation-based fluorescence lifetime measurements. Results indicate that frequency domain fluorimetry is useful to resolve stereomeric compounds for determination without physical separation. The precision of the measurements gives RSD values of 5.2% and 4.0% for CD and CN, respectively. Detection limits with the modulation fluorescence lifetime method were 11.3 and 17.2 μM for CD and CN, respectively.