Structural characterization and isomer differentiation of chalcones by electrospray ionization tandem mass spectrometry

A series of chalcones were characterized by electrospray ionization tandem mass spectrometry (MS(n)). Several ionization modes were evaluated, including protonation, deprotonation and metal complexation, with metal complexation being the most efficient. Collision-activated dissociation (CAD) was used to characterize the structures, and losses commonly observed include H(2), H(2)O, CO and CO(2), in addition to methyl radicals for the methoxy-containing chalcones. CAD of the metal complexes, especially [Co(II) (chalcone-H) 2,2'-bipyridine](+), allowed the most effective differentiation of the isomeric chalcones with several diagnostic fragment ions appearing upon activation of the metal complexes. MS(n) experiments were performed to support identification of some fragment ions and to verify the proposed fragmentation pathways. In several cases, MS(n) indicated that specific neutral losses occurred by stepwise pathways, such as the neutral loss of 44 u as CH3* and HCO*, or CH(4) and CO, in addition to CO(2).