Mass Fragmentation Characteristics of 4 Synthetic Cathinone Isomers

Synthetic cathinones, the designer analogs of the naturally occurring cathinone found in Khat, largely entered the recreational drug market at the end of the 2000s. They are a large class of new psychoactive substances (NPS) often used as substitutes for cocaine, which may cause psychostimulant and hallucinogenic effects and a number of fatalities worldwide. N-Ethylpentylone, one of the most famous synthetic cathinones on the clandestine market, was controlled in China since September 1, 2018. Recently, three uncontrolled isomers of N-ethylpentylone, namely hexylone, dipentylone and N-propylbutylone, were identified in the suspected samples. In order to investigate the mass fragmentation characteristics of synthetic cathinones with similar chemical structures, the four isomers were analyzed using gas chromatography-Orbitrap mass spectrometry (GC-Orbitrap-MS) and ultra high performance liquid chromatography-quadrupole time of flight-mass spectrometry (UPLC-QTOF-MS). High-resolution mass spectra were obtained by electron impact (EI) and electrospray ionization-collision induced dissociation (ESI-CID), and the structures and fragmentation pathways of main product ions were deduced. Under the EI mode, four isomers presented similar mass spectra with same base peak ion C6H14N+, which was originated from the α-cleavage of the C—N bond, the dominant fragmentation pathway of all synthetic cathinones. C8H5O3+ and C7H5O2+, the characteristic ions of cathinones with methylenedioxy substituted phenyl ring in the molecular structure, were also observed for all of them. However, there were variances in the low m/z ions generated by further cleavage of C6H14N+. Under the ESI-CID mode, the mass spectra were significantly different from each other, hence the alkyl substitution at different positions could be determined through the fragment ions generated by loss of H2O, amino groups and other groups from ［M+H］+. By investigating the mass spectrometric characteristics of the four isomers, their key distinguishing features were summarized, which provided a reference for the identification of synthetic cathinone, especially the substances with similar chemical structures.