Fused-silica capillaries of 50-µ internal diameter were packed with an «i-acid glycoprotein chiral stationary phase. The properties of electroosmosis in these packed capillaries were studied by investigating the influence of field strength, pH, and solvent composition on the velocity of electroosmotic flow. Direct enantiomeric separation by capillary electrochromatography was investigated with the use of these packed capillaries. Chiral resolution was achieved for the enantiomers of benzoin, hexobarbital, pentobarbital, ifosfamide, cyclophosphamide, disopyramide, metoprolol, oxprenolol, alprenolol, and propranolol. The effects of pH, electrolyte concentration, and concentration of organic solvents in the mobile phase on the retention and the enantioselectivity were studied.
INTRODUCTIONThe separation of enantiomers has long been a challenging field to analytical chemists. In recent years, there has been a rapidly increasing interest in chiral separations. It has been found that the enantiomers of chiral bioactive molecules often differ in potency, toxicity, pharmacological actions, and metabolism.1 Therefore, the ability to rapidly and accurately separate and determine the enantiomeric composition of chiral compounds is becoming increasingly important in pharmaceutical industry, food science, and agricultural chemistry, and in the last decade there has been a tremendous impetus to develop enantiomeric separation methods.Chiral separation by high-performance liquid chromatography (HPLC) using chiral stationary phases currently enjoys widespread popularity. Today, more than 50 different chiral stationary phases (CSPs) are commercially available for direct chiral separations. These CSPs may be subdivided into categories according to the type of chiral selector.1 2 One such category comprises a group of phases where immobilized proteins are used as chiral selectors. Of these, one of the most successful is that obtained by immobilizing «i-acid glycoprotein (AGP) on silica, introduced by Hermansson3 in 1983. The chiral selector, AGP, is an acidic protein (isoelectric point 2.7) with negatively charged aspartic acid residues and terminal serine group. Its positively charged groups are present in the arginine, lysine, and histidine residues. Chiral sites appear in the peptide chain, and also in the carbohydrate units that constitute 45% of the molecular weight.4 *AGP columns have been used for the direct enantiomeric sepa-
