Simultaneous Measurement of Phenobarbital, Phenytoin, Primidone, Ethosuximide,and Carbamazepine in Serum by High-Pressure

#{149}We present a method for simultaneously determining five anticonvulsants [phenobarbital, phenytoin (diphenylhy-dantoin), primidone, ethosuximide, and carbamazepine] in as little as 25 l of serum. The proteins are precipitated with an acetonitrile solution containing hexobarbital as an internal standard. The anticonvulsants are eluted from a reversed-phase column with a mobile phase consisting of an acetonitrile/phosphate buffer (19/81 by vol) at a flow rate of 3.0 mI/mm. The eluted drugs are detected by their absorption at 195 nm, and quantities estimated from their peak heights. Each analysis requires about 14 mm, at an optimum column temperature of 50 #{176}C.The lower limit of detection for all of these drugs is less than 10 ng. Sensi-tivities, for serum samples, of 1.0 mg/liter for all the drugs analyzed are attained routinely. Analytical recoveries fo