A mass spectrometer is used to:

  • Identify the presence of isotopes.
  • Measure the relative abundances of isotopes.
  • Measure relative atomic masses and relative molecular masses.
  • Identify unknown compounds.

Five stages of the spectrometer

  1. Vaporisation. The sample is injected as a gas, or as a liquid that is heated to vaporise it.
  2. Ionisation. An electron gun forms positive ions by bombarding the atoms with high-energy electrons which knock electrons off.
  3. Acceleration. The positive ions produces pass between a series of negatively charged plates. These plates accelerate these positive ions to high speeds.
  4. Separation. An electromagnet deflects ions towards the detector. The lighter ions are deflected the most.
  5. Detection. The detector responds to the ions that hit it and produces a signal that corresponds to the number of ions. A computer converts both measurements into a spectrum on a paper recorder. The series of peaks is called a mass spectrum.