Structural elucidation of tramadol, its derivatives, and metabolites using chemical derivatization and liquid chromatography–high‐resolution tandem mass spectrometry

Rationale Tramadol (T) is a strong painkiller drug that belongs to the opioid analgesic group. Several accidental intoxication cases after oral administration of T have been reported in the past decade. Tramadol, its derivatives, and metabolites present information‐limited mass spectra with one prominent peak representing the amine‐containing residue; therefore, their structural determination based on both electron impact mass spectrometry (EI‐MS) and ESI‐MS/MS spectra could be misleading. Methods A novel analytical method for the structural elucidation of tramadol, its four homologs, and its two main phase I metabolites ( N ‐desmethyltramadol and O ‐desmethyltramadol) was developed using chemical modification and liquid chromatography–high‐resolution tandem mass spectrometry (LC‐HR‐MS/MS) with Orbitrap technology. Results After chemical derivatization, each of the investigated T series exhibited informative mass spectra that enabled better exposition of their structures. The developed method was successfully implemented to explicitly identify the structures of tramadol and its N ‐desmethyltramadol metabolite in urine samples at low ng/mL levels. Conclusions An efficient derivatization‐aided strategy was developed for rapidly elucidating the structure of tramadol‐like compounds. The method is intended to assist forensic chemists in better diagnosing T and its analogs and metabolites in clinical or forensic toxicology laboratories.