Characterization of isomeric dimethylfuranocoumarins by electron impact ionization and surface and gaseous collision activation mass spectrometry

Abstract

Five dimethylfuranocoumarin isomers have been examined by conventional electron impact (EI) mass spectrometry and by collisional activation tandem mass spectrometry using collisions upon both gaseous and solid targets. Kiloelectron-volt collision-induced dissociation (CID) experiments were conducted upon the molecular cation (M+.), the molecular anion (M−.) and the protonated molecule ([M + H]+). Low-energy (electron-volt) CID and surface-induced dissociation (SID) experiments were performed on the molecular cation (M+.) as a function of collision energy in order to vary the internal energy deposited into the ion. Characteristic fragment ions were observed in the EI mass spectra of each isomer, which allowed for their clear distinction. High-energy CID performed on the molecular cation (M+.) yielded similar daughter ion spectra for each isomer, although small variations in the relative intensities of selected fragment ions allowed for their distinction. Nearly identical CID spectra were obtained for the molecular anions and protonated molecules. Low-energy CID performed upon the molecular cation under multiple-collision conditions at collision energies ranging from 10 to 29 eV yielded nearly identical daughter ion spectra for all but one isomer, suggesting that isomerization to a common ion structure may have occurred. By contrast, ion/surface (SID) collisions on M+. were highly effective in distinguishing the various isomers in that characteristic fragment ions were obtained for each compound. Remarkable features of the SID data are the extensive degree of fragmentation recorded for these aromatic molecules, and the reduced tendency of the activated ion to undergo rearrangement to a common ion structure.