Simultaneous HPLC determination of vigabatrin and gabapentin in serum with automated pre-injection derivatization

A simple and partially automated method for the HPLC determination of the new anticonvulsants vigabatrin and gabapentin in serum samples from epileptic patients is described. The first step in sample pre-treatment is the precipitation of the serum proteins using an excess of acetonitrile to which two internal standards have been added. After centrifugation the supernatant fraction of the samples was placed into an autosampler of an HPLC apparatus which can be programmed with different automatic procedures for pre-injection derivatizations. The amino acids vigabatrin and gabapentin are derivatized by reactions with ortho-phthaldialdehyde (OPA) and mercaptoethanol. The OPA derivatives are separated on a reversed phase column and measured by fluorimetry. Detection of the gabapentin derivatives requires careful removal of oxygen from the mobile phase by degassing continuously with helium. In this respect the fluorescence signal of vigabatrin derivatives is less sensitive to a loss in intensity by the back diffusion of oxygen into the mobile phase after degassing with helium for only a short time.