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The Mass Spectrometer

A mass spectrometer can be used to experimentally measure the percentage abundances of isotopes in a sample of an element.

  • The sample is placed in the mass spectrometer and vaporised
  • The vaporised sample is ionised to form positive ions.
  • The ions are accelerated by an electric field.
  • The degree of deflection by a magnetic field or the time of flight depends on the mass of the isotope
  • A detector detects the ions as a pulse or current. The greater the abundance the larger the signal.
  • The mass-to-charge or m/z ratio of all the signals is output as a mass spectrum.

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Specification: OCR Chemistry A (H032), AS-level, 2.1.1 Atomic structure and isotopes. Topic: Atoms, Ions and Compounds.

Key terms in this lesson

Isotopes
Atoms of the same element with the same number of protons but different numbers of neutrons.
Ion
A positively or negatively charged atom or group of atoms, formed by the loss or gain of electrons.

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