Enantiomeric separations of basic pharmaceutical drugs by micellar electrokinetic chromatography using a chiral surfactant, N-dodecoxycarbonylvaline

A novel surfactant with a chiral head group, (R)- or (S)-N-dodecoxycarbonylvaline (DDCV), was used to achieve enantiomeric separations of twenty basic pharmaceutical compounds by micellar electrokinetic chromatography (MEKC). Most of these compounds were beta-agonists (anti-asthmatic, broncodilators) or beta-antagonists (anti-hypertension, anti-angina). DDCV can separate polar as well as more hydrophobic chiral analytes in the same buffer system. The selectivities for these enantiomeric pairs range from 1.03 to 1.23 with good efficiencies. Separations utilizing DDCV are easy to optimize and allow for exact enantiomeric migration order reversal by switching the enantiomeric form of the surfactant. Buffer systems were assessed to minimize Joule heating and to optimize the repeatability of parameters such as migration time, relative migration time, selectivity, peak areas and area ratios. An electrolyte system consisting of 25 mM DDCV, 100 mM zwitterionic CHES (2-[N-cyclohexylamino] ethanesulfonic acid) and 10 mM triethylamine (TEA) was most effective for these runs, The precision for migration times, relative migration times and selectivities was better than 1%, 0.1% and 1% R.S.D., respectively, while the precision for the area ratios ranged from 1% to 4%. The possible effect of analyte structure on selectivity, efficiency and precision of peak area was studied.