Routine determination of eight common anti-epileptic drugs and metabolites by high-performance liquid chromatography using a column-switching system for direct injection of serum samples.

A simple and rapid high-performance liquid chromatographic method for determining eight common anti-epileptic drugs and metabolites in serum is described. A column-switching system including one analytical column and two precolumns for sample enrichment offers the possibility of directly injecting patients' sera without any pretreatment. The two precolumns are alternately switched over to avoid time loss in analysis due to the sample washing step. The samples are flushed with dilute phosphoric acid, as the purge liquid, onto the precolumns which consist of very short cartridges (length 0.5 cm) filled with spherical ODS silica gel (particle size 30 micron). The retained substances are carried over, after purification, onto the analytical column in the same direction of flow as in the flushing step. A mixture of acetonitrile and phosphoric acid--sodium phosphate buffer solution is thereby used as solvent for the gradient elution. The separation was carried out using an analytical column, which was filled with ODS material of particle size 5 micron.