Enantiomeric separations of benzodiazepines by electrochemically modulated liquid chromatography

Abstract

Electrochemically modulated liquid chromatography (EMLC) has been applied to the enantiomeric separation of a group of benzodiazepines (i.e., oxazepam, lorazepam and temazepam) using a porous graphitic carbon (PGC) stationary phase and β-cyclodextrin (β-CD) as a chiral mobile phase additive. The basis of the separation derives from the reversible electrosorption of the additive onto PGC, resulting in a new approach for manipulating the chirality and selectivity of the stationary phase. Changes in the voltage applied ( E appl) to the stationary phase were found to alter the retention and the enantioselectivity of the separation, both of which reflect the dependence of the electrosorption of the additive on E appl. By exploiting these dependencies, mixtures of each of the three racemates could be resolved to differing extents while using the same isocratic elution condition. A general description of the retention process and the role of the apparent enantiomerization of oxazepam and lorazepam are briefly discussed.