Rongying Wang, Xiaoning Lu, Mingjia Wu Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, National Analysis and Research Center of Electrochemistry and Spectroscopy, Changchun, Jilin 130022, China Chiral separation of promethazine by capillary electrophoresis with end-column amperometric detection Sensitive end-column amperometric detection has been successfully coupled to capillary electrophoresis for chiral separation of promethazine, with a carbon fiber microdisk electrode as working electrode. Baseline separation and sensitive detection were achieved under optimum conditions: 0.030 M Na 2 HPO 4 and 0.015 M citric acid at pH = 2.50, 1.0 mM b-CD, 10 kV separation voltage, and detection potential 1.10 V (vs Ag/AgCl). The numbers of theoretical plates were higher than 700 000, and the detection limit was 5610 –8 M. On-line treatment of the electrode has also been stud- ied and discussed. Key Words: Capillary electrophoresis; Amperometric detection; Chiral separation; Promethazine Ms received: March 16, 2000; revised: July 2, 2001; accepted: July 16, 2001 1 Introduction In recent years, there has been an unprecedented growth of interest in the separation of enantiomers of pharmaceu- tically and clinically important compounds. Apart from their optical characteristics, the physical and chemical properties of enantiomers are exactly the same so their separation is a challenge for analysts. Many methods such as GC and HPLC have been used for enantiomer separation. Recently, capillary electrophoresis (CE) has been found to be an ideal supplement to classical chroma- tography for the separation of enantiomers because of its high efficiency, short analysis time, flexibility of rapid incorporation of various selectors, and feasibility of method development [1]. A number of papers on enantio- mers separation by CE have appeared, in which a wide variety of chiral selectors have been employed, including proteins, modified crown ethers, antibiotics, chiral micelles, and cyclodextrins (CDs), or their derivatives. Among them CDs and their derivatives are the most popu- lar [2 – 5]. In most commercially available instruments, UV absor- bance is used for detection and it is the dominant detec- tion technique for chiral separation. Although the UV detector is reliable and easy to handle, it has an inherent disadvantage, i.e. a relatively high detection limit due to its short optical path length. Compared to the UV detector, the laser-induced fluorescence (LIF) detector has a higher sensitivity and seems to be the ideal solution for this pro- blem. However, the applicability of LIF is limited to com- pounds that fluoresce or compounds that can be deriva- tized with a fluorescent tag. Moreover, instruments with LIF detectors are rather expensive. Electrochemical detection (ED), especially amperometric detection with a microelectrode, which has a sufficient detection limit, good selectivity, and low instrument cost, is a promising approach to detection. Much work has been done on the determination of a variety of compounds by CE with ED [6 – 8]; however, very little [9, 10] has been done on detec- tion of enantiomers. Coupling electrochemical detection to chiral separation is a fairly new research field, and a good extension of CE – ED. This article is concerned with the chiral separation of pro- methazine followed by end-column amperometric detec- tion. A carbon fiber microdisk electrode, which is com- monly used in CE – ED because of its wide potential win- dow, easy treatment, and low price, was used as a work- ing electrode. A newly designed, home-made ampero- metric detection cell was used which was convenient for proper alignment of the capillary with the working elec- trode. Detection limit and column efficiency improved greatly compared to UV detection. The parameters that would affect separation and detection such as b-cyclodex- trin concentration, buffer pH and concentration, applied voltage and detection potential were studied and opti- mized. Treatment of the electrode on-line was also stud- ied and discussed. 658 Correspondence: Dr. Mingjia Wu, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, National Analysis and Research Center of Electrochemistry and Spectroscopy, Changchun, Jilin 130022, China. i WILEY-VCH Verlag GmbH, D-69451 Weinheim 2001 1615-9306/2001/0808–0658$17.50+.50/0 J. Sep. Sci. 2001, 24, 658–662