Evaluation of the synergistic effect with amino acids for enantioseparation of basic drugs using capillary electrophoresis.

The synergistic effect of two acidic amino acids, aspartic and glutamic acid, on the electrophoretic enantioseparation of four basic drugs was evaluated in the BGE containing a CD and at different pHs. Chlorpheniramine, hydroxyzine, propranolol and tramadol were used as the basic model drugs. However, no enantioseparations were achieved with a BGE containing sole amino acid, but the combined use of an acidic amino acid and a CD showed improved enantioseparations (synergistic effect) compared with the single CD system. The results demonstrated that at optimized pH, the electrostatic interactions of the anionic amino acids with the positively charged basic drugs could result in a decrease of the analyte migration velocity and it consequently improved the enantioseparation. The effective parameters such as the amino acid and chiral selector type and concentration, buffer pH, applied voltage, and capillary temperature were optimized. Favorable enantiomeric resolution and migration times of the model drugs were achieved with a 100 mM phosphate buffer solution (pH 3.0) containing 5.0 mM HP-α-CD/HP-β-CD and 20 mM aspartic acid with an 18 kV applied voltage at 25°C. 1 H NMR experiments were also carried out in a mixture of an analyte and CD in the absence and presence of aspartic acid. The NMR results were consistent with the results obtained by CE which showed the synergistic effect of amino acid.