Science & Technology in Action

1st Edition

Working with Mass Spectrometry

Higher Education Authority

The function of the Mass Spectrometer is covered in this lesson. The concept of the isotope is described and the physics of the instrument in separating isotopes is described. The process of testing is explained and some practical applications of spectrometry are described.
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Contains the full lesson along with a supporting toolkit, including teachers’ notes.

Lesson excerpt

What is a mass spectrometer?
The mass spectrometer is an instrument widely used by chemists, geologists, biologists, physicists and forensic scientists to determine the relative molecular mass of atoms and molecules. The spectrometer was invented in 1919 by Francis W Aston while working in the world famous Cavendish Laboratories in Cambridge under JJ Thompson, the man who discovered the electron. 

What is relative molecular mass?
The relative molecular mass of a substance is defined as the sum of the relative atomic masses of the atoms in a molecule. However, not all atoms of a particular element have the same mass. Such atoms are called isotopes.

Frederick Soddy coined the phrase isotope while working with lead 206, 207 and 208 which are formed when uranium decays radioactively. He found that atoms of the same element can have the same number of protons but different numbers of neutrons.

Isotopes have the same number of protons therefore the sameAtomic Number. However, they have different numbers ofneutrons and therefore have different Mass Numbers. He was awarded the Nobel Prize in 1921 for this work. 

Aston initially worked with neon. Using his mass spectrometer, he was eventually able to show that almost all elements haveisotopes. In fact, he used the mass spectrometer to discover 212 of the 278 naturally occurring isotopes or nuclides. He was awarded the Nobel Prize for his work in 1922.

Quiz questions

  1. The Mass Spectrometer was invented by Albert Einstein. false
  2. Isotopes of the same element have the same relative atomic mass false
  3. Isotopes were discovered by Frederick Soddy. true
  4. When high energy electrons hit a sample molecule they knock protons false
  5. In the magnetic field heavy particles and deflected more than light ones false
  6. Heavy particles are separated because they fall under the influence of gravity false
  7. A spectrograph shows mass on the horizontal axis and abundance on the vertical axis true
  8. A substance is vaporised before introduction to the mass spectrometer true
  9. Aston did his initial work on neon. true
  10. All elements have isotopes. true