2B4 Instrumental techniques

• Mass spectrometry

  • molecules may fragment as a result of electron bombardment
  • fragments rearrange to become stable
• Fragmentation

  • collision with an electron from the electron gun
  • forms two particles, one is a cation and the other is a neutral radical
  • the species is a radical cation
  • the collision seriously weakens the bonds in the particles and should not be surprised that it easily fragments
  • weaker bonds will fragment first and give rise to bigger peaks
  • the same molecule can fragment in different ways depending on where its hit
  • fragments must come from the breakage of one bond only
• Analysing mass spectra

  • find the relative molecular mass by finding the highest m/z value
  • can be made complex by the presence of chlorine, bromine or carbon-13