The mass spectrometer gives accurate information about relative isotope mass and about relative abundance of isotope.
- It is kept under high vacuum so that the ions do not collide with the air particles, which might stop them from reaching the detector.
- The sample must be in gaseous state. If it is solid than it is vaporised first by heating.
Ionisation- beam of electrons from 'electron gun' knocks out electrons from atoms or molecules so they form positive ions.
Acceleration- positive ions are attracted to the negatively charged plates and are accelerated to a high speed- the lighter the ion the faster it goes.
Deflection- The magnetic field deflects the beam of ions to form a curve. Heavier ions are deflected less than the lighter ones. The stronger the field the greater the deflection.
Detection- Ions strike the detector, accept electrons, lose their charge and create a current which is proportional to their abundance.
A computer works out the value- mass/charge ratio. Mass spectrum is produced.
Mass spectrometry can be used to identify elements (planetary space probes). It can also be used to determine relative molecular mass.
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