Formation of odd-electron product ions in collision-induced fragmentation of electrospray-generated protonated cathinone derivatives: aryl α-primary amino ketones.

RATIONALE: Modification of the even-electron rule for fragmentation reactions of protonated molecules (even electron ions) may be necessary to interpret the liquid chromatography/mass spectrometry (LC/MS) spectra of aryl α-primary amino ketones as new designer drugs.
METHODS: Collision-induced fragmentation of 38 protonated cathinone derivatives generated by electrospray ionisation (ESI) was examined by hybrid quadrupole time-of-flight mass spectrometry (Q-TOF MS).
RESULTS: Q-TOF MS revealed that odd-electron product ions are often formed by collision-induced dissociation (CID) of protonated aryl α-primary amino ketones, contradicting the even-electron rule. Radical cations were among the most characteristic and most abundant ions in the CID-MS/MS product spectra, and were usually represented by basic peaks in the spectra.
CONCLUSIONS: To help elucidate the correct structures of new aryl α-primary amino ketone drugs by LC/MS/MS, it is essential to include odd-electron product ions in the data interpretation rules. Even and odd numbers of valence electrons in the product ions should be allowed in data interpretation.