Table 3–

Ionization methods used in mass spectrometry.

Method	Fundamental principle
ESI‐MS	The ions are produced from a peptide contained in a solvent (for example, an organic compound such as methanol or acetonitrile) that is scattered in a fine aerosol
FAB‐MS	The peptide analyzed is mixed with a matrix, which is a non volatile reagent of protection (glycerol, diethanolamine, and triethanolamine, among others), and is bombarded with a beam of high‐energy atoms (4000 to 10000 eV) in a vacuum. Atoms are of an inert gas such as argon or xenon
MALDI‐MS	The peptide analyzed is bombarded by a laser beam (nitrogen), while a matrix (sinapinic acid) is used to protect the peptide. The matrix allows avoiding direct contact of the peptide with the beam, facilitating its vaporization, and ionization