Separation of enantiomers by affinity electrokinetic chromatography using avidin

Avidin, a basic protein isolated from egg white, was employed as a chiral selector in affinity electrokinetic chromatography (EKC) for the separation of acidic enantiomers. Optical isomers of vanilmandelic acid, warfarin, ibuprofen, ketoprofen, flurbiprofen, and folinic acid were successfully resolved within 20 min with 25 microM avidin in a linear polyacrylamide-coated capillary under weakly acidic conditions. The effects of pH, the concentration of avidin, addition of an organic solvent such as ethanol and 2-propanol, and temperature on enantioselectivity were investigated. The choice of pH and the organic solvent additive was critical to improve the separation. Some general considerations about affinity EKC are also described, based on a simple one-site interaction model.