Rapid and sensitive determination of nalmefene in human plasma by gas chromatography–mass spectrometry

A rapid gas chromatography–mass spectrometric method for the determination of nalmefene in human plasma is described. The procedure involves protein precipitation, extraction with ethanol–chloroform mixture and derivatization with pentafluropropionic anhydride. The deuterated analog of nalmefene, 6β-naltrexol-d7, was used as the internal standard. Quantitation was achieved on a HP-1 column (12 m×0.2 mm I.D.) with negative chemical ionization (NCI) using methane:ammonia (95:5) as the reagent gas. The standard curves were fitted using a quadratic equation with the curve encompassing a range of 0.5 to 200 ng/ml, and the intra- and inter-assay variations for three different nalmefene levels were less than 10% throughout. The limit of quantitation was found to be 0.5 ng/ml. The method described is highly specific and reproducible, and could also be applied for the determination of naltrexone and 6β-naltrexol. Application of the method to actual human plasma samples is demonstrated.