Electrosorption based modification of porous graphitic carbon: Use of electrochemically modulated liquid chromatography to create a chiral stationary phase for enantiomeric separations

A novel approach for the modification of the separation capabilities of electrochemically modulated liquid chromatography is described. The basis of the approach derives from the electrosorption of an organic additive from the mobile phase onto a porous graphitic carbon (PGC) stationary phase, resulting in a new dimension in the ability to alter reversibly the chemical composition at the surface of the stationary phase. The viability of the approach is demonstrated by the enantiomeric separation of racemic mixtures of the pharmaceutical agents hexobarbital and mephenytoin. These separations are achieved by the electrosorption of the organic additive P-cyclodextrin to form a PGC surface that is coated with a chiral selector. Results indicate that changes in applied potential can not only manipulate the effectiveness of these separations but can also reverse the enantiomeric elution order. A general mechanism for these separations is proposed and the potential applicability of the strategy to other types of LC separations is briefly noted.