Four‐sector tandem mass spectrometry: A comparison of the molecular and quasi‐molecular ions of the cyclic depsipeptide valinomycin formed using electron impact, chemical ionization, fast atom bombardment, field desorption and electrospray lonizatfion

Abstract Four‐sector tandem mass spectra of the molecular and quasi‐molecular ions of the cyclic depsipeptide valinomycin (RMM 1110.6) were compared. Electron impact (EI), chemical ionization (CI), fast atom bombardment (FAB), field desorption (FD) and electrospray ionization were used to create M+˙, [M + H]+, [M + Na]+ and [M + K]+ ions from valinomycin. Large differences were found between the FD and FAB tandem mass spectra of [M + Na]+ ions, and between the FD and EI tandem mass spectra of M+˙ ions. Differences between the spectra are ascribed to the formation of ions having the same mass but different structures. FAB tandem mass spectra of [M + Na]+ and [M + K]+ ions show greater degrees of fragmentation than do the FAB tandem mass spectra of [M +H]+ ions.