Use of vancomycin silica stationary phase in packed capillary electrochromatography I. Enantiomer separation of basic compounds

Chiral separation of basic compounds was achieved by using 75 or 100 mum ID fused-silica capillaries packed with a vancomycin-modified diol silica sta tionary phase. The capillary was firstly packed for about 12 cm with a slur ry mixture composed of diolsilica (3:1) then with the vancomycin modified d iol-silica (3:1) (23 cm), and finally with diol-silica (3:1) for about 2 cm . Frits were prepared by a heating wire at the two ends of the capillary; t he detector window was prepared at 8.5 cm from the end of the capillary whe re vancomycin was not present. The influence of the mobile phase compositio n (pH and concentration, organic modifier type and concentration) on the ve locity of the electroosmotic flow, chiral resolution and enantioselectivity was studied. Good enantiomeric resolution was achieved for atenolol, oxpre nolol, propranolol, and venlafaxine using a mobile phase composition of 100 mM ammonium acetate solution (pH 6)/water/acetonitrile (5:5:90 v/v/v) whil e for terbutaline a mixture of 5:15:80 v/v/v provided the best separations. The use of methanol instead of acetonitrile caused a general increase of e nantiomer resolution of the studied compounds together with a reduction of efficiency and detector response. However, the combination of acetonitrile and methanol in the mobile phase las, e.g., 10% methanol and 80% acetonitri le) allowed to improve the enantiomer resolution with satisfactory detector response.