[Chiral separation of doxazosin and its intermediate by capillary electrophoresis using tetramethylammonium hydroxide...

A capillary electrophoretic method for the enantiomeric separations of doxazosin and its intermediate was developed. Several tetraalkylammonium reagents were examined for controlling the electroosmotic flow in order to improve resolution of the enantiomers. Tetramethylammonium hydroxide (TMB) was found more suitable than tetrabutylammonium hydroxide (TAB) or hexadecyltrimethylammonium bromide (CTAB) for the enantiomer separation. In addition, the effects of the pH value, the separation voltage and the concentration of the sodiumdihydrogen phosphate on the chiral separation were investigated. A buffer containing 60 mmol/L sodium dihydrogen phosphate (pH 2.2), 30 mmol/L TMB and 12 mmol/L beta-cyclodextrin (beta-CD) resulted in the baseline separation of the doxazosin enantiomers and its intermediate enantiomers. It showed that the presence of TMB was essential in some chiral separations that were previously not achieved by only using the beta-CD as a chiral selector.