Differentiation of homologous and regioisomeric methoxy-cathinone derivatives by GC–MS, MS/MS and GC–IR

Abstract

A combination of GC–MS, MS/MS and GC–IR techniques can be used to differentiate the nine methoxy cathinone derivatives related to the designer drug MDPV. Nine homologous and regioisomeric methoxyphenyl-aminoketone cathinone derivatives were prepared from the three commercially available 2-, 3- and 4-methoxybenzaldehydes. The gas chromatographic separation of the nine precursor methoxyphenones was achieved on a 100% dimethyl polysiloxane (Rtx®-1) stationary phase and the regioisomeric aminoketones were resolved on a 5% diphenyl, 95% dimethyl polysiloxane (Rtx®-5) stationary phase. The chemical ionization mass spectra (CI–MS) show only one major peak occurring at the mass of the protonated molecular ion (M+1)+ while the EI–MS spectra display primarily the iminium cation fragment. The MS/MS product ion spectra for the three homologous iminium cations yield a homologous series of ions representing the loss of 42Da from the parent species. MS/MS experiments confirmed the loss of 42Da occurring via pyrrolidine ring fragmentation for iminium cations having the methyl and ethyl side-chains and via side-chain fragmentation for the n-propyl side-chain. The vapor phase infrared spectra in the range of 1300–1150cm−1 show unique and characteristic absorption pattern for each of the three regioisomeric methoxy-group substitution patterns.