The Mass Spectrometer

The mass spectrometer is a device used to study isotopes of ions produced in a cathode ray
tube. Isotopes of an element share the same chemical properties but have different masses and produce different values for their charge-to-mass ratio. An electron beam strikes vapor atoms that yield positive ions accelerated by a potential difference and deflected by a uniform magnetic field to hit a photographic plate. Mass spectrometry can also be used to identify molecules by analyzing the masses of its fragments.


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The charge-to-mass ratio of an ion can be derived from Newton's second law and the Lorenz force, yielding
where is the charge, is the mass, is the potential difference, is the magnetic field intensity, and is the radius of gyration.
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