DETERMINATION OF ETHOSUXIMIDE IN PLASMA BY DERIVATIZATION AND HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A simple and sensitive liquid chromatographic method is described for the determination of ethosuximide in plasma as a highly sensitive deri vative. Ethosuximide in plasma, after separation with isopropanol extr action, was derivatized with strong chromophore reagent, 4-bromomethyl -7-methoxy-coumarin. The resulting derivatives were separated on a Nov a-Pak C18 column with water-acetonitrile-methanol(60:20:20, v/v) as th e mobile phase. The linear range for the determination of ethosuximide in spiked plasma was over 2-40 nmol. The limit of detection for ethos uximide was about 7.0 +/- 1.2 pmol per 20 mu L injection (S/N= 5). The intraday relative standard deviation (n = 6) and the interday relativ e standard deviation (n = 12) were all less than 2.5% for ethosuximide . The recovery for ethosuximide in plasma was greater than 96%.