Mass Spectrometer

  • Created by: SophieHW
  • Created on: 03-03-15 17:51

Mass Spectrometer

The mass spectrometer can be used to determine all the isotopes present in a sample of an element and therefore to identify elements.

1. Ionisation

  • A vapourised sample is injected at low pressure
  • An electron gun fires high energy electrons at the sample
  • This knocks out an outer electron
  • Forming positive ions with a different charges

2. Acceleration

  • A negative electric field accelerates the positive ions and makes them into a beam

3. Deflection

  • The beam of positive ions is deflected by a strong magnetic field
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Mass Spectrometer

  • The degree of deflection depends on the mass/charge ratio, m/z
  • The smaller this ratio the larger the deflection
  • By varying the magnetic field ratio, ions of different m/z ratios pass through the centre

4. Detection

  • The ions reach the detector and generate a small current, which is fed to a computer for analysis.
  • The size of the current is proportional to the abundance of the species.

It needs to be under a vacuum otherwise air particles would ionise and register on the detector.

If the sample is not vapourised then vaporizing it would be the first step.

The heavier the ion the less it is deflected.

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Mass Spectrometer


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