QUANTITATIVE-DETERMINATION OF BUTORPHANOL AND ITS METABOLITES IN HUMAN PLASMA BY GAS-CHROMATOGRAPHY ELECTRON-CAPTURE NEGATIVE-ION CHEMICAL-IONIZATION MASS-SPECTROMETRY

Two separate analytical methods have been developed for the determinat ion of butorphanol and its metabolites in human plasma. One method is specific for butorphanol (I) while the other determines the metabolite s, hydroxybutorphanol (II) and norbutorphanol (III). Both procedures i ncorporate solid-phase extraction, chemical derivatization and separat ion, and detection using gas chromatography-electron-capture negative- ion chemical ionization mass spectrometry (GC-ECNCI-MS). Both methods use the cyclopropyl analog of I (BC-2605, IV) as the internal standard and the procedures for extraction of the analytes from plasma are ide ntical. However, following extraction, either the pentafluorobenzoyl e ster of I or the tris- and bis-trifluoroacetyl esters of II and III, r espectively, were prepared. The derivatives were analyzed by GC-ECNCI- MS with selected-ion monitoring of the molecular ions. The standard cu rves were linear over the concentration ranges of 20-2000, 20-1000 and 50-1000 pg/ml for I, II and III, respectively. All standard curves fr om the assay validation had r(2) values of greater than or equal to 0. 994, 0.991 and 0.985 for I, II and III, respectively. For all three co mpounds, the intra- and inter-assay precisions (C.V.) and inter-assay accuracy (deviation from nominal) were within 12% for plasma quality c ontrol samples. All derivatives were stable in the reconstitution solv ent for at least 24 h. The assays are being used for the determination of plasma concentrations of I, II and III in humans following repeate d administration of nasal spray.