Formation of [M+15]+ ions from aromatic aldehydes by use of methanol: in-source aldolization reaction in electrospray ionization mass spectrometry

Unexpected [M?+?15]+ ions were formed during the analysis of aromatic aldehydes by use of methanol in positive-ion electrospray ionization mass spectrometry. Aromatic aldehydes with electron-withdrawing groups or electron-donating groups were all tested to make sure the universality. All the aromatic aldehydes studied with methanol as the solvent could generate [M?+?15]+ ion, and for most of them, the [M?+?15]+ ion was more intense than the [M?+?H]+ ion. Deuterium-labeling experiment, high-performance liquid chromatographyMS experiment, collision-induced dissociation experiment, and theoretical calculations were performed to identify the formation of [M?+?15]+ ion. The proposed reaction mechanism is a gas-phase aldol reaction between protonated aromatic aldehydes and methanol occurring in electrospray source. Understanding and using this unique gas-phase ion/molecule reaction can indeed offer a novel and fast approach for the direct identification of aromatic aldehydes. Copyright (C) 2011 John Wiley & Sons, Ltd.