Identification of Designer Drugs using Gas Chromatography High-Resolution Mass Spectrometry and A Soft-Ionization Source

A small set of amphetamines has been analyzed by gas chromatography (GC) high-resolution time-of-flight mass spectrometry (TOFMS) using a microplasma photoionization (MPPI) soft-ionization source. This plasma-based, wavelength selectable ionization source enables ionization of the test compounds and their corresponding derivatives at ~8-12 eV that is a softer alternative to electron ionization at 70 eV. Three plasma gases were used in this study: Xe plasma that emits photons at resonance lines of 9.57 eV and 8.44 eV; Kr plasma at 10.63 eV and 10.02 eV, and Ar plasma at 11.82 eV and 11.61 eV. 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 amphetamines yield primarily iminium ions, which make the identification of the test compounds by GC-TOFMS inconclusive. The MPPI mass spectra of the TFA-derivatized amphetamines yield abundant molecular ions, when using Xe as plasma gas, and enough fragment ions with the Ar plasma that can help in formula generation. The structure elucidation of two “known unknowns” designer drugs using this “tunable” soft-ionization source and a high-resolution TOF mass spectrometer is presented in this study.