Capillary electrochromatography, chiral selectors

DK Lloyd, S Li, P Ryan. Protein chiral selectors in free-solution capillary electrophoresis and packed-capillary electrochromatography. J Chromatogr A 694 285-296, 1995. 

Olsson and Blomberg [141] enantioseparated omeprazole and its metabolite 5-hydroxyomeprazole using open tubular capillary electrochromatography with immobilized avidin as chiral selector. The separation was performed with open tubular capillary electrochromatography. The protein avidin was used as the chiral selector. Avidin was immobilized by a Schiffs base type of reaction where the protein was via glutral-dehyde covalently bonded to the amino-modified wall of a fused-silica capillary, 50 /an i.d. Both racemates were baseline resolved. Resolution... 

The chiral SO is coated to the capillary wall. This technique is known as open-tubular electrochromatography (OT-EC) )5(X)1. Enantioselective OT-EC methods have been described for CDs 1277), proteins ).501), polysaccharides )5021 and terguride [503] as chiral selectors. The main disadvantage is the low loading capacity, and therefore this technique has not gained high popularity. 

CD). The partial-filling technique (PFT) proved to be a suitable and efficient approach to avoid MS source contamination, as well as signal suppression due to nonvolatile additives. Therefore, fhe PFT technique is particularly adapted with chiral selectors added into fhe electrolyte solution. Because of fhe counter-current contribution, charged chiral selectors were found to be more suitable for the online MS detection of separated enantiomers. Capillary electrochromatography with chiral stationary phases has also been developed, but to a lesser extent. 

There are two general approaches for the separation of enantiomers [1-4,28-32]. The direct method is based on the formation of transient diastereomer association complexes with a chiral selector immobilized in the stationary phase, or added to the mobile phase. The former approach requires the use of special stationary phases (section 10.4) while the later uses conventional stationary phases with special additives included in the mobile phase (section 10.5). When preparative applications are contemplated the use of immobilized chiral selectors is the more common approach. Method selection also depends on the choice of the separation mode. Table 10.2. While chiral stationary phases are the only choice for gas chromatography [16,28,33-38], and are used almost exclusively for supercritical fluid chromatography [39-43] and capillary electrochromatography [44-47], they also dominate the practice of liquid chromatography... 

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