Schematic of a magnetic-sector mass spectrometer
The ion optics in the ion-source chamber of a mass spectrometer extract and accelerate ions to a kinetic energy given by:
K.E. = 0.5 mv2 = eV
where m is the mass of the ion, v is it's velocity, e is the charge of the ion and V is the applied voltage of the ion optics.
The ions enter the flight tube between the poles of a magnet and are deflected by the magnetic field, H. Only ions of mass-to-charge ratio that have equal centrifugal and centripetal forces pass through the flight tube:
mv2 / r = Hev
centrifugal = centripetal forces.
Where r is the radius of curvature of the ion path:
r= mv / eH
This equation shows that the m/e of the ions that reach the detector can be varied by changing either H or V.
Double Focusing analyzers:
An electrostatic analyzer is added in this type of instrument to separate particles with difference in kinetic energies.
/chem-ed/ms/mag-sect.htm, updated 2/5/97
Copyright © 1996 by Brian M. Tissue, all rights reserved.
Science Hypermedia Home Page