Enantiomer separation of N-protected amino acids by non-aqueous capillary electrophoresis and high-performance liquid chromatography with tert.-butyl carbamoylated quinine in either the background electrolyte or the stationary phase

A non-aqueous CE method was developed for evaluating the chiral discrimination potential of cinchona alkaloids and different kinds of carbamoylated derivatives of quinine and quinidine type chiral selectors towards acidic analytes, in particular a series of various Bz (benzoyl), DNB (3,5-dinitrobenzoyl) and DNZ (3,5-dinitrobenzyloxycarbonyl) amino acid derivatives. In this study, the enantioselectivity values obtained in non-aqueous CE with tert.-butyl carbamoylated quinine as chiral additive have been compared with the values found for the same series of selectands in HPLC using the same selector immobilized onto silica as chiral stationary phase. Similarly to the background electrolyte used in CE an ethanol–methanol mixture (60:40, v/v) containing 100 mM octanoic acid and 12.5 mM ammonia has been selected as HPLC mobile phase. Under these conditions, a good correlation (r=0.954) between the enantioselectivities observed with the two techniques has been obtained. Thus the non-aqueous CE method can be applied as a screening tool for the rapid evaluation of the chiral discrimination potential of a large set of newly developed chiral selectors derived from quinine and related alkaloids.