Chiral anion exchangers applied to capillary electrochromatography enantioseparation of oppositely charged chiral analytes: investigation of stationary and mobile phase parameters

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.…”

Enantioseparation of Neutral Compounds on a Quinine Carbamate-Immobilized Zirconia in Reversed-Phase Capillary Electrochromatography

“…ACN was chosen as the organic solvent as it usually gives a faster and better separation in CEC. 25,27,48 Directions of EOF for both bare zirconia and QNZ are cathodic within the pH range from 4 to 6. Phosphate ions as Lewis bases are able to bind strongly to the Lewis acid sites on zirconia surface to provide negative surface charges 34 and hence cathodic EOF, regardless of the mobile phase pH.…”

“…6 in methanol-acetate buffer mobile phases. 25,27 It is very likely that the phosphate anions adsorb onto silica surface to a greater extent than acetate anions and the negative charges from adsorbed phosphate and dissociated silanol groups effectively cancel out the positive charges on amino groups of quinine moiety, leaving net negative charge on the surface. EOF on QNZ is greater than that on QNS.…”

“…[3][4][5][6] CSPs based on the use of carbamoylated derivatives of QN and quinidine as anionexchange type selectors were found to be highly stereoselective for the direct resolution of chiral acids in reversed-phase LC [7][8][9][10][11][12][13][14][15][16][17][18][19][20] and CEC. [21][22][23][24][25][26][27] Chiral recognition mechanism on carbamoyl QNimmobilized stationary phases in organic-aqueous buffer mobile phases involves simultaneously ion pairing, and differential hydrogen bonding (HB), π-π and van der Waals interactions between carbamoyl QN and enantiomers of the chiral analyte. 8,28 Ion pairing interaction is much stronger than the remaining stereoselective interactions and is essential in the chiral recognition processes.…”

“…8,28 Ion pairing interaction is much stronger than the remaining stereoselective interactions and is essential in the chiral recognition processes. 8,25,27 An example from an earlier work shows that an acidic chiral analyte (N-3,5-dinitrobenzoyltryptophn) that is present in the form of anions at the pH of the mobile phase is more retained (k1 = 19.13) and well separated (α = 5.17) while its nonacidic derivative (N-3,5-dinitrobenzoyltryptophn methyl ester) is much less retained (k1 = 9.47) and not enantioseparated at all (α = 1.00). 8 On the 18-crown-6-2,3,11,12-tetracarboxylic acid-bonded CSPs, which have been widely used for the separation of primary amino compounds and the chiral recognition mechanism on it is known to require complexation interactions between primary ammonium ions and crown oxygens, successful enantioseparations were obtained for secondary amines that do not strongly bind to crown ether oxygens, 29 and for the analytes with no primary or secondary amino groups that can be protonated and undergo complexation interactions with the crown moiety.…”