Cyclodextrins as enantioselective mobile phase modifiers for chiral capillary electrophoresis. Effects of pH and...

When cyclodextrins (CDs) are used as enantioselective mobile phase modifiers for capillary electrophoresis, optimization of chiral resolution is usually carried out by varying operational parameters such as the choice of CD type, CD concentration and pH of the operating buffer. This work describes the effects of the above variables on the resolution of five chiral basic pharmaceuticals with different functional groups, using three different beta-cyclodextrin (BCD) modifiers (BCD, 2-hydroxypropyl BCD and methyl BCD). In order to more clearly determine the specific role of pH, CD type and CD concentration on chiral resolution, the running buffers used in this work contained only the buffer salts and enantioselector. Very good resolution was achieved for chlorpheniramine and terbutaline; propranolol was able to be partially resolved. The degree of resolution achieved for these compounds is explained by examining the balance of specific and non-specific interactions between the solutes and the BCDs. Although the migration behavior of atropine and metoprolol indicates that they undergo marked interactions with the cyclodextrins in the running buffer, these interactions were not enantioselective, and these solutes were unable to be optically resolved under any of the conditions in our study.