Structural elucidation of phenidate analogues possessing a secondary amine residue via derivatization and LC-MS/MS analysis

Tamar Shamai Yamin, Analytical Chemistry, IIBR, Ness Ziona, Israel (tamarsh@iibr.gov.il)
Hagit Prihed, Analytical Chemistry, Iibr, Ness Ziona, Israel
Avi Weissberg, Analytical Chemistry, Iibr, Ness Ziona, Israel

Continued diversification of phenidate-based new psychoactive substances (NPS), provides sustained challenges for forensic chemists who request to identify new substances for which no reference standard or analytical data are available. We report a new analytical technique for the structural elucidation of phenidate analogues i.e., methylphenidate (Ritalin^®), its major metabolite ritalinic acid (RA), 3,4-dichloromethylphenidate (3,4-DCMP) and its hydrolysis product 3,4-dichlororitalinic acid (3,4-DCRA), based on “in vial” chemical derivatization with isobutyl chloroformate (IBCF) in both aqueous and organic solutions, followed by liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS/MS). These four representative analogues possess a secondary amine residue, which leads to a major/single amine-representative fragment/product ion at m/z 84, both in their GC-EI-MS and LC-ESI-MS/MS spectra, making their identification ambiguous. In contrast, the resulting carbamate derivatives alter the charge distribution during ESI-MS/MS fragmentation and promote rich fragmentation patterns with full coverage of all parts of the molecule, enabling detailed structural elucidation and unambiguous identification of the original compounds, at low ng/ml levels. The method can be implemented to various phenidate analogues and may facilitate their identification.