Structural elucidation of phenidate analogues via the ESI-MS/MS spectra of their sodium adduct ions

The identification of phenidate new psychoactive substances (NPS) by implementing MS (Mass spectrometry) techniques is a challenging task. Phenidate analogues present information-poor mass spectra, both in GC-EI-MS and LC-ESI-MS/MS of the protonated molecules [M+H]⁺, with a high abundance fragment/product ion representing the secondary amine-containing residue. This lack of EI-MS and ESI-MS/MS information is attributed to the strong tendency of the amine residue to stabilize the positive charge and leads to unavoidable ambiguity in the identification process. Moreover, thermal decomposition of these compounds occurs in the injection port and/or on the column under standard GC conditions. Herein, we demonstrate how structural information can be attained instantaneously through the LC-ESI-MS/MS fragmentation of the accompanied sodium adducts [M+Na]⁺. The sodium cation alters the charge distribution during ESI-MS/MS fragmentation, generating a major product ion corresponding to the Na⁺ adduction of the carbonyl group, providing new structural information of the main core of phenidate derivatives (alkylaryl acetate/acetic acid), enabling their reliable structural elucidation. This quick, simple and easy technique can be implemented to confirm the identity or identify various structurally related phenidate analogues in forensic toxicology and doping analysis without the need for sample handling.