What are isotopes and how do they affect a mass spectrum?
Isotopes are atoms of an element with a different number of neutrons. These play a very important role in mass spectrometry. For example, C-13 occurs at about 1% of the natural abundance of Carbon. This would mean that for every 100 carbons in a molecule, there would statistically be one C-13. Therefore the relative height of the +1 m/z peak for a molecular ion in a mass spectrum is a reasonably accurate measure of the number of carbons in the molecule. This assumes there are no metals present – as many metals have a complex distribution of isotopes (e.g. Tin or Ruthenium). Famous isotopic ratios are Chlorine, Bromine and Silver. When an analyte contains a complex distribution of isotopes, the observed isotope distribution will be unique and by comparison with the theoretical isotope distribution (calculated at the same resolution) is a very useful method of double checking the formula of the ion being measured.
