A simple method is described for adjusting the mobile phase composition to obtain optimum separation of commonly prescribed antiepileptic drugs by high-performance liquid chromatography. The drugs are separated, in less than 6 min, on a column of Hypersil ODS 5 μm (100 mmx5 mm i.d.) with a high mobile phase flow rate. The final mobile phase composition is a mixture of methanol, acetonitrile, tetrahydrofuran and water, adjusted to give the best separation with our laboratory conditions. The method is described and evidence of precision and accuracy presented. The improved separation resolves the major metabolites of carbamazepine which have been ignored in most methods for antiepileptic drugs. The advantages of mobile phase optimisation to improve the separation of antiepileptic drugs are discussed.
