The 4-bromo analogue (25B-NBOMe) and related halogenated derivatives of N-(2-methoxy)benzyl-2,5-dimethoxyphenethylamine (25-NBOMe) are a class of psychedelic drugs. This study examined how electron-donating groups (halogen and dimethoxy) influence the decomposition pathway of the distonic molecular radical cation during electron ionization mass spectrometry (EI-MS) of trifluoroacetamide (TFA) derivatives. Six regioisomeric dimethoxybenzyl-substituted analogues for four series of phenethyl aromatic ring substitution patterns were prepared, derivatized, and analyzed via gas chromatography coupled with EI-MS. The analogues yield two unique radical cation fragments.
Three drugs of abuse—MDEA, MDMMA, and MBDB—and seven additional side chain regioisomers share the same molecular weight (207) and major mass spectral fragments (m/z 72 and 135/136), making them difficult to distinguish by routine mass spectrometry. The authors evaluated trifluoroacetyl, pentafluoropropionyl, and heptafluorobutryl derivatives of the primary and secondary amines using gas chromatography-mass spectrometry. These derivatives produced significantly individualized mass spectra with unique fragment ions that allowed specific side chain identification. Trifluoroacetyl and heptafluorobutryl derivatives provided the most specific ions for distinguishing the compounds, and all perfluoroacyl derivatives showed reasonable resolution on the polar Rtx-200 stationary phase.