MASS SPECTRAL FRAGMENTATION OF CATHINONES BY HIGH-RESOLUTION TOFMS USING A SOFT
IONIZATION SOURCE

A set of 25 cathinones has been analyzed by GC high-resolution time-of-flight mass spectrometry (TOFMS) using a soft ionization source, referred in here as the microplasma photoionization (MPPI) source. This plasma-based, wavelength-selectable ionization source enables softer (i.e., ~ 8 to 12 eV) ionization of the test cathinones relative to electron ionization at 70 eV. Plasma gases such as Xe, Kr, and Ar, which generate distinct vacuum ultraviolet (VUV) resonance lines (i.e., Xe @ 8.44/9.57 eV, Kr @ 10.03/10.64 eV, and Ar @ 11.62/11.83 eV), have been evaluated for the identification of underivatized and derivatized cathinones. Derivatization of the test compounds with trifluoroacetic anhydride and α-methoxy-α-(trifluoromethyl)- phenylacetyl pyrazole was evaluated because the MPPI mass spectra of the underivatized cathinones yield primarily immonium ions and are identical to those obtained by electron ionization, thus leading to inconclusive MS identification of the test compounds. The MPPI mass spectra of TFA-derivatized cathinones yield both benzoyl and immonium ions, and certain TFA-derivatized cathinones yield molecular ions especially when using Xe as plasma gas, thus making possible their identification by MS.