In a mass spectrometer, the five processes involved are described as follows:

(a) Vaporisation:
Sample is vaporised under low pressure.

(b) Ionisation:
A high energy beam of electrons is used to displace (knock) an electron from the molecule to form a radical cation known as the molecular ion.

If the molecular ion is too unstable then it can fragment to give other smaller ions.

(c) Acceleration in an external electric field:
The collection of ions is then focused into a beam and accelerated into the magnetic field.

(d) Deflection in an external magnetic field:
The ions are deflected along circular paths according to the masses of the ions. The smaller the mass-to-charge (m/e) ratio, the greater the deflection. By adjusting the magnetic field, the ions can be focused on the detector and recorded.

(e) Detection of ions is registered and recorded as a mass spectrum.