3. Ion source characteristics

The gaseous ions are formed in the ionization source by a succession of processes which must be adapted to the nature of the sample, and which will help define the type of ionization source used. Ultimately, the ions are directed via a potential difference to the mass spectrometer's vacuum analyzer, either directly after their formation, or via an interface at atmospheric pressure. The different types of ion source used in organic mass spectrometry can be classified according to the four routes described in figure 6 . They can be identified in terms of :

• gas-phase ionization source (channel a) ;

• pneumatically assisted electrospray ionization (channel b);

• ionization/desorption...