Mass Spectrometer[]
Mass spectrometer
A mass spectrometer is a device which is used to measure the relative numbers of molecules and atoms of different masses. The mass spectrometer is a physical way of analysing elements and the mass of the particles that create them. Previously chemical methods were used but these proved less accurate than the measurements using a mass spectrometer.
Components of the mass spectrometer include:
Ion Chamber,
Velocity Selector,
Momentum Selector,
Ion Detector.
Measuring the mass[]
Once the ions have been acclerated to the same velocity in the velocity selector they enter the momentum selector. There is no electric field present but instead a magnetic field, the centripetal force on the ions is provided by the magnetic force,
BQv=mv(2)/r Flux Density x Charge x velocity = mass x velocity squared / radius
The radius of the Ion beam's path is given by
r=mv/BQ
The ion beam consists of singly ionised particles of constant velocity travelling in a unifrom magnetic field. Thus radius is directly proportional to mass. This is an extremly effective way of distinguishing between different isotopes of an element - allowing the relative abundance of the isotopes to be found from the relative densities of the signals detected by the detector.