Enantiomeric separation of N-protected amino acids by non-aqueous capillary electrophoresis using quinine or tert-butyl carbamoylated quinine as chiral additive

A capillary electrophoretic (CE) method for the enantioseparation of N-prot ected chiral amino acids was developed using quinine and tert-butyl carbamo ylated quinine as chiral selectors added to nonaqueous electrolyte solution s (NACE).A series of various N-derivatized amino acids were tested as chira l selectands, and in order to optimize the CE enantioseparation of these co mpounds, different; parameters were investigated: the nature of the organic solvent, the combination of different solvents, the nature and the concent ration of the background electrolyte, the selector concentration, the capil lary temperature, and the applied voltage. The influence of these factors o n the separation of the analyte enantiomers and the electroosmotic now was studied. Generally, with tert-butyl carbamoylated quinine as chiral selecto r, better enantioseparations were achieved than with unmodified quinine. Op timum experimental conditions were found with a buffer made of 12.5 mM ammo nia, 100 mM octanoic acid, and 10 mM tert-butyl carbamoylated quinine in an ethanol-methanol mixture (60:40 v/v). Under these conditions, DNB-Leu enan tiomers could be separated with a selectivity factor (a) of 1.572 and a res olution (Rs) of 64.3; a plate number (N) of 127,000 and an asymmetry factor (As) of 0.93 were obtained for the first migrating enantiomer. (C) 1999 Wi ley-Liss, Inc.