Sensitized Enantioselective Laser-Induced Phosphorescence Detection in Chiral Capillary Electrophoresis

The sensitivity of enantioselective cyclodextrin-induced room-temperature phosphorescence detection of camphorquinone (CQ) is enhanced using sensitization via a donor with a high extinction coefficient. The enantiomeric distinction is based on the different phosphorescence lifetimes of (+)-CQ and (-)-CQ after their complexation with alpha-cyclodextrin (alpha-CD). The collisional Dexter energy transfer from the selected donor 2,6-naphthalenedisulfonic acid (2,6-NS) to the acceptor CQ is still very efficient despite the inclusion of the acceptor into CD. For coupling to the chiral separation of (+/-)-CQ in cyclodextrin-based electrokinetic chromatography, the donor was added to the deoxygenated background electrolyte that consisted of 20 mM alpha-CD, 10 mM carboxymethyl-beta-CD, and 25 mM borate buffer at pH 9.0. Time-resolved batch studies on sensitized phosphorescence show a significant enantioselectivity for (+)- and (-)-CQ in the presence of both alpha-CD and CM-beta-CD although the lifetime difference is somewhat reduced with respect to direct excitation. The enantiomers were distinguished after their separation using an online lime-resolved detection system. Excitation was performed at 266 nm with a pulsed, small-sized, quadrupled Nd:YAG laser. With 1 x 10(-5) M 2,6-NS, limits of detection of 4.1 x 10(-8) M and 5.2 x 10(-8) M were found for (+)-CQ and (-)-CQ, respectively. The online measured lifetimes were 238 +/- 8 mu s for (+)-CQ and 126 +/- 10 mu s for (-)-CQ. The method was used to determine the concentration of (+/- )-CQ leaching from a cured dental resin into water. The extracts contained 4.7 +/- 0.1 x 10(-7) M of both (+)-CQ and (-)-CQ.