Identification of dihydroetorphine in biological fluids by gas chromatography-mass spectrometry

A method for the monitoring of dihydroetorphine hydrochloride, a powerful anaesthetic and analgesic drug, in biological fluids was developed, involving GC-MS with multiple selected-ion monitoring. Dihydroetorphine was extracted from human blood and urine with dichloromethane and then derivatized with N-heptafluorobutyrylimidazole after having been concentrated to dryness. A dihydroetorphine monoheptafluorobutyl derivative was formed, which showed good behaviour in GC-MS with electron impact ionization. Its molecular ion, m/z 609, and its main fragments, m/z 576, 534, 522 and 508, were selected as the ions for identification owing to their relative peak intensities and characteristics. The target drug was identified based on its retention time, its selected multiple ions and their relative intensities. This method was successfully used for the detection of dihydroetorphine in blood and urine from a dihydroetorphine addict and a poisoned patient, respectively.