Mass spectrometry

• Molecular ion peak - peak with the highest mass to charge ratio (m/z) in the mass spectrum, the M peak.
• 1. A sample is bombarded with electrons to produce a positive ion.
• 2. The ion is accelerated by an electric field.
• 3. The ion passes through a magnetic field to deflect it:

  higher mass = less deflection
• 4. A sensor then detects and records the ions reaching it.
• 1. Ionisation
  2. Acceleration
  3. Deflection
  4. Detection
• Molecular ion:

  • consists of the whole molecule, minus one electron
  • mass is the same as the relative molecular mass of the molecule
  • the ion with the heaviest mass (furthest to right)
  • electron collides with a molecule and knocks an electron off, resulting in a positively charged ion
• M+1 peak:

  • molecular ion with a mass 1 unit heavier than the normal molecular ion
  • usually caused by the presence of one atom of carbon 13 in the molecule, in place of much more abundant carbon 12 isotope
  • carbon 13 has an abundance of 1.1% of carbon atoms