Sensitized Enantioselective Laser-Induced Phosphorescence Detection in Chiral Capillary Electrophoresis Ivonne Lammers, Joost Buijs, Freek Ariese,* and Cees Gooijer Department of Biomolecular Analysis and Spectroscopy, Laser Centre, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands The sensitivity of enantioselective cyclodextrin-induced room-temperature phosphorescence detection of cam- phorquinone (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 r-cyclodextrin (r-CD). The collisional Dexter energy transfer from the selected donor 2,6-naphthalenedisul- fonic 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 r-CD, 10 mM carboxymethyl--CD, and 25 mM borate buffer at pH 9.0. Time-resolved batch studies on sensitized phosphorescence show a significant enantiose- lectivity for (+)- and (-)-CQ in the presence of both r-CD and CM--CD although the lifetime difference is somewhat reduced with respect to direct excitation. The enantiomers were distinguished after their separation using an online time-resolved detection system. Excitation was performed at 266 nm with a pulsed, small-sized, quadrupled Nd: YAG laser. With 1 × 10 -5 M 2,6-NS, limits of detection of 4.1 × 10 -8 M and 5.2 × 10 -8 M were found for (+)- CQ and (-)-CQ, respectively. The online measured lifetimes were 238 ( 8 µs for (+)-CQ and 126 ( 10 µs 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 × 10 -7 M of both (+)-CQ and (-)-CQ. Enantiomers may show completely different behaviors in living organisms such as differences in uptake, distribution, metabolism, excretion, toxicity, and pharmaceutical effects. 1 Chirality is, therefore, very important in many fields of analytical chemistry including biomedical, pharmaceutical, environmental, agricultural, and food analysis. 2,3 For example, in dentistry, the chiral com- pound camphorquinone (CQ) is often used as a photoinitiator for the polymerization of visible light-cured restorative resins. 4 The leaching of CQ from cured or uncured composite resins has recently been investigated with gas or liquid chromatography coupled to mass spectrometry. 5-7 However, no distinction was made between the two enantiomers of CQ although these might have different effects in living systems. For example, the degrada- tion of (-)-CQ is significantly slower than the degradation of its mirror image (+)-CQ in yeast and rabbits. 8,9 Here, we demonstrate the enantioselective analysis of (±)-CQ extracted from a cured composite resin using capillary electrophoresis (CE) and sensi- tized enantioselective phosphorescence detection. This novel analytical approach increases the detection sensitivity consider- ably, while the enantioselectivity is retained. Cyclodextrin-induced room-temperature phosphorescence (CD- RTP) can be used as an enantioselective detection technique. 10-12 For example, the formation of 2:1 (host/guest) inclusion com- plexes of R-cyclodextrin (R-CD) with (+)-CQ or (-)-CQ provides a different degree of protection against quenching in deoxygenated aqueous samples. This results in a substantial difference between (+)-CQ and (-)-CQ regarding their phosphorescence intensity and lifetime. 11 Recently, we showed the coupling of this detection method to cyclodextrin-based electrokinetic chromatography (CD- EKC) to distinguish the CQ enantiomers based on both migration time and phosphorescence lifetime. 13 For the chiral separation of (±)-CQ, a dual cyclodextrin system is needed consisting of neutral R-CD and negatively charged carboxymethyl--cyclodex- trin (CM--CD). 8 In contrast to R-CD, no enantioselective RTP signal is obtained for the diastereomeric complexes of (+)-CQ or (-)-CQ with CM--CD. However, the difference between the phosphorescence decay curves of the two enantiomers in a * To whom correspondence should be addressed. Fax: +31 (0) 20 5987543. E-mail: f.ariese@few.vu.nl. (1) Smith, S. W. Toxicol. Sci. 2009, 110, 4–30. (2) Kumar, A. P.; Jin, D.; Lee, Y. I. Appl. Spectrosc. Rev. 2009, 44, 267–316. (3) Ward, T. J.; Baker, B. A. Anal. Chem. 2008, 80, 4363–4372. (4) Van Landuyt, K. L.; Snauwaert, J.; de Munck, J.; Peumans, M.; Yoshida, Y.; Poitevin, A.; Coutinho, E.; Suzuki, K.; Lambrechts, P.; van Meerbeek, B. Biomaterials 2007, 28, 3757–3785. (5) Alvim, H. H.; Alecio, A. C.; Vasconcellos, W. A.; Furlan, M.; de Oliveira, J. E.; Saad, J. R. C. Dent. Mater. 2007, 23, 1245–1249. (6) Michelsen, V. B.; Moe, G.; Skålevikc, R.; Jensen, E.; Lygre, H. J. Chro- matogr., B 2007, 850, 83–91. (7) Rogalewicz, R.; Batko, K.; Voelkel, A. J. Environ. Monit. 2006, 8, 750– 758. (8) García-Ruiz, C.; Siderius, M.; Ariese, F.; Gooijer, C. Anal. Chem. 2004, 76, 399–403. (9) Robertson, J. S.; Hussain, M. Biochem. J. 1969, 113, 57–65. (10) García-Ruiz, C.; Hu, X.; Ariese, F.; Gooijer, C. Talanta 2005, 66, 634–640. (11) García-Ruiz, C.; Scholtes, M. J.; Ariese, F.; Gooijer, C. Talanta 2005, 66, 641–645. (12) Zhang, X. H.; Wang, Y.; Jin, W. J. Anal. Chim. Acta 2008, 622, 157–162. (13) Lammers, I.; Buijs, J.; van der Zwan, G.; Ariese, F.; Gooijer, C. Anal. Chem. 2009, 81, 6226–6233. Anal. Chem. 2010, 82, 9410–9417 10.1021/ac101764z  2010 American Chemical Society 9410 Analytical Chemistry, Vol. 82, No. 22, November 15, 2010 Published on Web 10/21/2010