EI(Electron Ionization)

The EI sources is used for organic MS.

The gas-phase molecules are introduced to the EI sources

Disadvantage: extensive fragmentation

The IC is contructed as below:

The sample is in gaseous phase

The electron source: from filament heated by High voltage applied potential.

A wavelength is assigned to each electron and given by:

The kinetic energy of electron in a range: 20eV to 70eV corresponding to the wavelenght 2.7 to 1.4 A.

Because at the low electron accelerating potentials, the energy of lectrons is lower than the molecule ionization energy, and at the high electrong accelerating potentials, the molecules become "transparent" to electrons, so the potentials must be selected to give the kinetic energy ranged from 20eV to 70eV.