Enhanced detection of flavonoids by metal complexation and electrospray ionization mass spectrometry

Metal complexation with the use of an auxiliary ligand is explored as an al ternative to conventional protonation or deprotonation for analysis of a se ries of flavonoids by electrospray ionization mass spectrometry, Use of a n eutral auxiliary ligand, 2,2'-bipyridine, results in formation of [M-II(fla vonoid - H)bpy](+), ternary complexes with intensities that are 2 orders of magnitude greater than the corresponding protonated flavonoids and up to 1 .5 orders of magnitude greater than the deprotonated flavonoids, based on c onfirmation by collisionally activated dissociation patterns. The formation of ternary complexes with six divalent transition metals, Co2+, Ni2+ CU2+, Zn2+, Mn2+, and Fe2+ were compared. Cu2+ resulted in the most intense comp lexes and simplest mass spectra, while Co2+ gave the second most intense sp ectra and also produced two key products that could be useful for a selecte d ion monitoring strategy. Complexation with iron(III) bromide is also inve stigated to explore the feasibility of using triply charged metals.