Field desorption mass spectrometry of quaternary ammonium salts: Cluster ion formation

The field desorption mass spectra of salts such as quaternary ammonium and carbenium salts with organic cations in addition to high cation intensities show signals for cluster ions composed of the salt cation + salt molecule, i.e. [C + n M] + , n = 1–5, thus allowing determination of the molecular weights of salts. In some cases cluster ions of the type [ n M – 1] + are detected. Conditions for the formation of cluster ions are discussed.