Magnetic -Deflection or Sector Mass Analyzer:

In a magnetic deflection mass spectrometer, ions leaving the ion source are accelerated to a high velocity. The ions then pass through a magnetic sector in which the magnetic field is applied in a direction perpendicular to the direction of ion motion. When acceleration is applied perpendicular to the direction of motion of an object, the object's velocity remains constant, but the object travels in a circular path. Therefore, the magnetic sector follows an arc; the radius and angle of the arc vary with different ion optical designs.

 

A magnetic sector alone will separate ions according to their mass-to-charge ratio. Only ions of a single m/z value will have the proper trajectory leading to the exit slit ahead of the detector. By changing the magnetic field strength, ions with differing m/z values are brought to focus at the detector slit.

The ions velocity ‘υ’, in the magnetic field is given by

Limitation:

In a single-focusing magnetic sector instrument there is a lack of uniformity of ion energies, since the accelerating potential experienced by an ion depends on the region at which it is formed in the ionization chamber. The resulting spread in ionic energies produces a spread in their radii of curvature in the magnetic field. The result is peak broadening and low to moderate resolution.

½ m υ ²  =zV

However, the resolution will be limited by the fact that ions leaving the ion source do not all have exactly the same energy and therefore do not have exactly the same velocity.