Trace analysis of ethosuximide in human plasma with a chemically removablederivatizing reagent and high-performance liquid chromatography

A simple and sensitive liquid chromatographic method is described for the d etermination of ethosuximide in human plasma, as a highly sensitive derivat ive. Ethosuximide spiked in plasma was extracted with toluene and derivatiz ed with a chemically removable derivatizing reagent, 2-(2-naphthoxy)ethyl 2 -[1-(4-benzyl)piperazyl]ethanesulfonate in a homogeneous system, using magn esium oxide as base catalyst. The resulting derivative was separated on a L iChrospher diol column with 1.2% isopropanol in n-hexane as the mobile phas e and using coumarin as the internal standard. Several parameters affecting the extraction/derivatization of ethosuximide from spiked plasma were inve stigated. The linear range for the determination of ethosuximide in spiked plasma was over 30-700 nmol/ml. For ethosuximide in plasma, the detection l imit (signal-to-noise ratio=3; sample size, 10 mu l) was about 9 pmol; the relative standard deviation was 6.4% for intra-day assay (n = 6) and 9.2% f or inter-day assay (n = 6) and the relative recovery was found greater than 94%. (C) 1999 Elsevier Science B.V. All rights reserved.