Enantiomer separation by nonaqueous and aqueous capillary electrochromatography on cyclodextrin stationary phases

Abstract

Native beta- and gamma-cyclodextrin bound to silica (ChiraDex-beta and ChiraDex-gamma) were packed into capillaries and used for enantiomer separation by capillary electrochromatography (CEC) under aqueous and nonaqueous conditions. Negatively charged analytes (dansyl-amino acids) were resolved into their enantiomers by nonaqueous CEC (NA-CEC). The addition of a small amount of water to the nonaqueous mobile phase enhanced the enantioselectivity but increased the elution time. The choice of the background electrolyte (BGE) determined the direction of the electroosmotic flow (EOF). With 2-(N-morpholino) ethanesulfonic acid (MES) or triethylammonium acetate (TEAA) as BGE an inverse EOF (anodic EOF) was observed while with phosphate a cathodic EOF was found. The apparent pH (pH*), the concentration of the BGE, and the nature of the mobile phase strongly influenced the elution time, the theoretical plate number and the chiral separation factor of racemic analytes.

Sensitive chiral analysis by capillary electrophoresis

“…Stationary phases previously employed in chiral HPLC, such as CDs and their derivatives [37,38], macrocyclic antibiotics [39], proteins [26], polysaccharides [40][41][42], and ligand-exchange type selectors [43] (see Table 1) have been adapted for chiral CEC using packed capillary columns. Open-tubular capillary columns have been the less used for the enantiomeric separation of chiral compounds by CEC.…”

The covalently bonded cellulose tris(3,5-dimethylphenylcarbamate) on a silica monolithic capillary column for enantioseparation in capillary electrochromatography☆

“…These columns suffer from low phase ratio, ease of overloading, and low sensitivity in UV detection. In particulates packed column, the CSPs were packed into the capillaries and restricted by the retaining frits, such as CD and its derivatives [2][3][4], protein [5], macrocyclic antibiotic [6], chiral polyacrylamides [7], and Pirkletype CSP [8]. These columns have a high-phase ratio and high enantioselectivity, but the bubble formation and poor repeatability caused by the supporting frits retarded the application of particulate packed column in CEC for the practical routine analysis of enantiomers.…”

Recent progress in capillary electrophoretic analysis of amino acid enantiomers

“…In the P-CEC mode, CSs bonded silica particles are packed into the capillary. To obtain the chiral discrimination of amino acids, the capillaries packed with ␤-and ␥-CDs [130], teicoplanin aglycone [131], 3,5-dinitrobenzoyl (DNB)-phenyl Gly [132], DNB-npGly [133], (S)-N-(DNB)leucine-N-phenyl-N-propylamide [134,135] and 18C6H 4 [136] bonded silica particles have been prepared. By using nonaqueous BGSs in the (S)-N-(DNB)leucine-N-phenyl-N-propylamide bonded silica capillaries, the CEC separation of aromatic amides of amino acid can be achieved through enantioselectivedonor-acceptor interactions between the CSs and the analytes in the normal phase [134] and polar organic modes [135].…”