Features of EI

EI is the most widely used ionization mode in GC/MS analysis. Almost all commercial GCMS instruments equip this mode as standard ionization.
EI causes much fragmentation of a molecule whose spectral pattern is useful for identifying sample compound.
Library search is available. EI mass spectra obtained by 70eV electron bombardment can be used for identification by comparing with spectra registered in the mass spectral library.
An open type of ion source is used. Vacuum pressure inside the source, mainly determined by carrier gas, is about less than 10-2 Pa.