Abstract: Objective To study the identification method for 4’-F-4-methylaminorex（4’-F-4-MAR） in samples without reference substance. Methods Gas chromatography-mass spectrometry （GC-MS）, ultrahigh-performance liquid chromatography-quadrupole time-of-flight-mass spectrometry （UPLC-QTOFMS）, nuclear magnetic resonance （NMR） and Fourier transform infrared （FTIR） were comprehensively used for the structure identification of 4’-F-4-MAR in samples. Results Under the positive electrospray ionization （ESI + ） mode, quasi- molecular ion in the first order mass spectrometry of the unknown compound was 195.092 6 and its molecular formula was inferred to be C10H11FN2O. The fragment ions in the mass spectrometry of the unknown compound were compared with the related fragment ions of 4,4’-dimethylaminorex （4,4’-DMAR） in literature. It was found that the main fragment ions of the unknown compound were all 4 bigger than the corresponding fragment ions of 4,4’-DMAR. Therefore, the unknown compound was inferred to be a 4,4’-DMAR analogue with a methyl substituted by a fluorine in the benzene ring. The equivalent protons at δ=7.30 and δ=7.06 in 1H-nuclear magnetic resonance （1H-NMR） spectra and the characteristic spin-spin coupling constants （1JC- F=245.2 Hz, 2JC-F= 21.3 Hz, 3JC-F=8.1 Hz） for 13C-19F interactions in carbon spectra, further proved that the fluorine substituted methyl at the para-position of the benzene ring. Finally, the unknown compound was determined as 4’-F-4-MAR. Conclusion A method that comprehensively used the identification materials 4’-F-4- MAR in GC-MS, UPLC-QTOF-MS, NMR and FTIR is established and the fragmentation mechanism of fragmentation ions of 4’- F- 4- MAR created under the two modes -- electron impact （EI） and electrospray ionization under collision induced dissociation（ESI-CID）is deduced. The information will assist forensic science laboratories in identifying this compound or other substances with similar structure in their case work.

Key words: forensic toxicology, new psychoactive substance, gas chromatography- mass spectrometry, spectroscopy, Fourier transform infrared, nuclear magnetic resonance, aminorex, 4’- F- 4- methylaminorex（4’-F-4-MAR）