Mass Spectrometry

Key Principles of Mass Spectrometry

  • Mass spectrometry is a technique used to determine the molecular mass of a sample.
  • It involves the ionisation of a sample, where the molecules are converted into charged ions.
  • These ions are then separated based on their mass-to-charge ratio.
  • The resulting pattern of fragments is called a mass spectrum, which provides a unique ‘fingerprint’ of the molecule which can be used for its identification.

Process of Mass Spectrometry

  • The sample to be analysed is inserted into the mass spectrometer and is then vaporised to form gaseous atoms or molecules.
  • The gaseous molecules are then ionised by bombarding them with high-energy electrons.
  • This ionisation process results in the formation of positively charged ions.
  • The positive ions are then accelerated by an electric field before they are deflected by a magnetic field. The extent of deflection depends on their mass-to-charge ratio.
  • These ions are then detected and a mass spectrum is produced which shows the relative abundance of each ion type.

Interpreting Mass Spectra

  • The x-axis of a mass spectrum represents the mass-to-charge ratio of the ions, while the y-axis represents the relative abundance of each ion.
  • The peak farthest to the right, known as the molecular ion peak or parent peak, corresponds to the ion with the highest m/z value, which gives the molecular mass of the original molecule.
  • Peaks to the left of the molecular ion peak represent fragment ions formed by the breakdown of the original molecule.
  • The relative positions, heights and shapes of the peaks in the mass spectrum can indicate the structure and isotopic composition of the molecule being analysed.

Applications of Mass Spectrometry in Polymer and Life Science

  • Mass spectrometry is widely used in the identification and quantitative analysis of polymers and biomolecules.
  • In polymer chemistry, mass spectrometry can be used to identify and quantify the different monomers that make up a polymer.
  • In biochemistry, mass spectrometry can be used to determine the sequence of amino acids in a protein, or to identify an unknown compound in a complex biological sample.
  • In medical and forensic science, mass spectrometry can be used for drug testing, or to identify and quantify potentially harmful toxins in a sample.