Since only ions can be analyzed, ionization is an important component of MS. Electron ionization (EI) and photoionization (PI) are two commonly used ionization techniques. In EI, high energy (70 eV) electrons from an electron beam collide with the vaporized sample, resulting in the formation of a radical cation. The energy imparted in these collisions is enough to induce bond cleavage and the formation of fragment ions.