A rapid electron-capture gas chromatographic procedure for the analysis ofp-hydroxymephenytoin

An electron-capture gas chromatographic procedure was developed for detecti on and quantification of p-hydroxymephenytoin (OHMEP), a metabolite of S-me phenytoin, in human liver microsomal preparations. OHMEP was derivatized wi th pentafluorobenzoyl chloride (PFBC) under basic aqueous conditions prior to analysis on a gas chromatograph equipped with a capillary column and an electron-capture detector. Dextrorophan was carried through the procedure a s internal standard. The structure of the PFB derivative was confirmed usin g combined gas chromatography-mass spectrometry (GC-MS). The procedure is r apid and reproducible and produces a stable derivative that has excellent c hromatographic properties. The limit of detection was less than 5 ng/ml, an d the method was applied to extracts of human liver microsomes, which had b een incubated with S-mephenytoin [a probe substrate for cytochrome P450 (CY P) 2C19]. (C) 2001 Elsevier Science Inc. All rights reserved.