Ion‐trap mass spectrometry in ion structure studies. 1. Characterization of isomeric hydroxyindoles by electron ionization and energy‐resolved collision‐activated mass spectrometry

Three hydroxyindole isomers were investigated by conventional electron ionization (EI) mass spectrometry and by collision‐activation (CA) experiments. Although the EI mass spectra of the three isomers are virtually superimposable, 3‐hydroxyindole can easily be differentiated from the others by single‐energy collision spectroscopy. Only by energy‐resolved mass spectrometry (ERMS) could the characterization of the 4‐ and 5‐ hydroxyindole isomers be achieved. ERMS, which in the ion‐trap mass spectrometer can be performed by different methods, was achieved by changing both the AC supplementary voltage and the βz value at which the collision experiments were performed. The first method proved to be the most effective in the present case. Further collision experiments, carried out at a range of AC voltage durations did not yield energy‐resolved data.