Separation of Enantiomers by Capillary Electrophoresis

Many chiral selectors have been nsed for chiral separations in CE. The most widely used are discussed below. Most of these chiral selectors are also applied in HPLC, as will be discnssed later. 

FIGURE I Structures, shapes and dimensions of the native a, P and ] CDs (adapted from Reference 91). 

In general, charged CDs have shown superior discrimination abilities, especially the highly-sulfated (HS-CDs) ones. Furthermore, the separation mechanism is altered by the introduction of electrostatic interactions. Finally, the use of chiral selectors carrying a charge opposite to that of the analytes can greatly improve the mobility difference between the two enantiomers. The use of mixtures of CDs in chiral separation is also possible.  

Numerous applications of chiral separations using CDs can be found in the literature. Some examples, either reviewing chiral separations in CE or presenting the separation of several compounds, can be found in References 97,101,107,121-124. Several studies related to the chiral separation of amino-acid derivatives by CE and micellar electrokinetic capillary chromatography with different types of CDs have also been reported 102,103,114,125-128 

The main drawback in chiral separation methods using derivatized CDs is that these selectors are mainly available as complex mixtures that contain a large number of isomers differing in their degree of substitution, which may result in batch-to-batch selectivity differences.The use of pure single enantiomers or very reproducible mixtures is thus required to obtain reproducible and robust methods. 

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F Lelievre, C Gueit, P Gareil, Y Bahaddi, H Galons. Use of zwitterionic cyclodextrin as a chiral agent for the separation of enantiomers by capillary electrophoresis. Electrophoresis 18 891-896, 1997. 

X Wang, JT Lee, DW Armstrong. Separation of enantiomers by capillary electrophoresis using pentosan polysulfate. Electrophoresis 20 162-170, 1999. 

Tanaka, Y. Otsuka, K. Terabe, S. Separation of enantiomers by capillary electrophoresis-mass spectrometry employing a partial filling technique with a chiral crown ether. J. Chromatogr., A 2000, 875, 323-330. 

Maruszak, W, MG Schmid, G Gtibitz and E Ekiert (2004). Marek trojanowicz separation of enantiomers by capillary electrophoresis using cyclodextrins. Methods in Molecular Biology, 243,275-289. 

Electrophoresis. - A review on the use of chiral glycosidic surfactants for the separation of enantiomers by capillary electrophoresis has been published. A considerable increase in the reliability of identifying compounds by capillary electrophoresis has been achieved by a reduction in the standard deviation of migration times of various compounds, including tetramethylrhodamine-label-led oligosaccharides, from >3% to <0.04%. ... 

J Haginaka. Enantiomer separation of drugs by capillary electrophoresis using proteins as chiral selectors. J Chromatogr A 875 235-254, 2000. 

Ishibushi K, Izumoto S, Nishi H, Sato T (1997) Enantiomer separation of denopamine by capillary electrophoresis with charged and uncharged cyclodextrins. Electrophoresis 18 1007-1012... 

Koppenhoeffer, B., Epperlein, U., Zhu, X., Lin, B. Separation of enantiomers of drugs by capillary electrophoresis. IV. Hydroxypropyl-y-cyclodextrin as chiral solvating agent. Electrophoresis 1997, 18, 924—930. 

Rodriguez de Pablos, R., Garcia-Ruiz, C., Crego, A. L., and Marina, M. L. (2005). Separation of etodolac enantiomers by capillary electrophoresis. Validation and application of the chiral method to the analysis of commercial formulations. Electrophoresis 26(6), 1106—1113. 

IE Valko, HAH Billiet, J Frank, KChAM Luyben. Factors affecting the separation of mandelic acid enantiomers by capillary electrophoresis. Chromatographia 38 730-736, 1994. 

H Matsunaga, J Haginaka. Separation of basic drug enantiomers by capillary electrophoresis using ovoglycoprotein as a chiral selector comparison of chi-... 

In contrast, CSPs have achieved great repute in the chiral separation of enantiomers by chromatography and, today, are the tools of the choice of almost all analytical, biochemical, pharmaceutical, and pharmacological institutions and industries. The most important and useful CSPs are available in the form of open and tubular columns. However, some chiral capillaries and thin layer plates are also available for use in capillary electrophoresis and thin-layer chromatography. The chiral columns and capillaries are packed with several chiral selectors such as polysaccharides, cyclodextrins, antibiotics, Pirkle type, ligand exchangers, and crown ethers. 

To establish chiral separation method for donepezil hydrochloride enantiomers by capillary electrophoresis (CE) and to determine the two enantiomers in plasma [39], alkalized plasma was extracted by isopropa-nol-n-hexane (3 97) and L-butefeina was used as the IS. Enantioresolution was achieved using 2.5% sulfated-beta-cyclodextrin as chiral selector in 25 mmol/1 triethylammonium phosphate solution (pH 2.5) on the uncoated fused-silica capillary column (70 cm x 50 fim i.d.). The feasibility of the method to be used as quantitation of donepezil HC1 enantiomers in rabbit plasma was also investigated. Donepezil HC1 enantiomers were separated at a baseline level under the above condition. The linearity of the response was evaluated in the concentration range from 0.1 to 5 mg/1. The linear regression analysis obtained by plotting the peak area ratio (A(s)/A(i)) of the analyte to the IS versus the concentration (C) showed excellent correlation coefficient The low limit of detection was 0.05 mg/1. The inter- and intra-day precisions (RSD) were all less than 20%. Compared with chiral stationary phase by HPLC, the CE method is simple, reliable, inexpensive, and suitable for studying the stereoseletive pharmacokinetics in rabbit. 

Bonato and Paias [136] developed two sensitive and simple assay procedures based on HPLC and capillary electrophoresis for the enantio-selective analysis of omeprazole in pharmaceutical formulations. Racemic omeprazole and (S)-omeprazole were extracted from commercially available tablets using methanol-sodium hydroxide 2.5 mol/1 (90 10). Chiral HPLC separation of omeprazole was obtained on a ChiralPak AD column using hexane-ethanol (40 60) as the mobile phase and detection at 302 nm. The resolution of omeprazole enantiomers by capillary electrophoresis was carried out using 3% sulfated /1-cyclodextrin in 20 mmol/1 phosphate buffer, pH 4 and detection at 202 nm. 

Issaq HJ, Chan KC. Separation and detection of amino acids and their enantiomers by capillary electrophoresis A review. Electrophoresis 1995 16 ... 

B Koppenhoefer, X Zhu, A Jakob, S Wuerthner, B Lin. Separation of drug enantiomers by capillary electrophoresis in the presence of neutral cyclodextrins. J Chromatogr A 875 135-161, 2000. 

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