Gas--liquid chromatographic microdetermination of underivatized ethosuximide (alpha-ethyl-alpha-methyl succinimide) in plasma or serum.

A gas-liquid chromatographic procedure for the microdetermination of ethosuximide is described. Ethosuximide is extracted from acidified plasma or serum into chloroform containing an internal standard alpha,alpha-dimethyl-beta-methyl succinimide. Part of the initial chloroform extract is gently evaporated, the residue redissolved in n-heptane at 60 degrees C, and an aliquot analyzed by gas-liquid chromatography. The procedure is rapid, reliable, sensitive, and specific. It requires a 25--50 microliter sample for a single estimation, has a detection threshold of less than 10 micromol/liter, and is suitable for routine clinical use.