1.3 Mass Spectrometer

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Ionisation

  • Vapourised - sample is turned ito a gaseous state as its easier to move through the chamber

  • Bombarded with electron - given a sufficient enough energy supply so that one or more electrons are knocked out of the outer most shell

  • most ions will only carry a +1 charge as its difficult to remove anelectron from an already positive ion
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Acceleration

The gaseous sample is passed through an electric field, as it accelorates the positive ions to a high speed as it goes through the chamber.

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Deflection

The amount an ion is deflected depends on the MASS/CHARGE RATIO

  • the mass of the ion - lighter ions are deflected more than heavier ions
  • the charge of the ion - the larger the charge the more the ion is deflected. an ion with a 2+ charge will be deflected more than an ion with a 1+ charge
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Detection

The beam of electrons passing through the chamber are detected electrically using  a detector.

Only ions with the correct mass/charge ratio are detected - the others are deflected too far and are eventually removed using a vaccum.

  • The signal is amplified and recorded

Initially a vacuum must be placed in the chamber to remove any unwanted ions - that werent deflected from a previous sample, or air molecules.This is so that the ions have a free runthrough the machine

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