The structure identification of a diphenhydramine-related impurity in methamphetamine

Some methamphetamine (MA) crystals contain pharmaceutical impurities resulting from the co-ingredients of medicines used for extracting ephedrine/pseudoephedrine. These pharmaceutical impurities and their related byproducts can reflect the trends in precursor chemicals and manufacturing sources. In this research, 1 pharmaceutical-impurity-related byproduct was detected in several seized MA samples synthesized by I/P (Nagai, Moscow, or Hypo) method. Its structure was postulated through the analysis of fragment ions in electron ionization (EI) mass spectrum. The impurity was further synthesized and analyzed using electrospray ionization-collision-induced dissociation (ESI-CID) mass spectrum and nuclear magnetic resonance (NMR), and finally determined to be N¹ ,N¹ ,N² -trimethyl-N² -(1-phenylpropan-2-yl)ethane-1,2-diamine. The impurity was inferred to be generated by the reaction of MA and the breakdown of diphenhydramine, a co-ingredient of medicines used for extracting ephedrine/pseudoephedrine. Simulation MA synthetic experiments via Nagai, Moscow, and Hypo methods using ephedrine and diphenhydramine as starting materials were performed to prove our presumption. The presence of the impurity indicates that these MA samples were manufactured from pharmaceutical containing ephedrine/pseudoephedrine and diphenhydramine.