Mass Spectrometry

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  • Created by: boggleme
  • Created on: 04-12-14 15:23
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  • Mass spectrometry
    • high energy electrons are fired from electron guns
      • compounds are ionised and can be accelerated, then deflected by a magnetic field
        • mass/charge ratio --> if this is larger, the ions will be deflected more
    • ions generally fragment but some will remain and this gives the molecular ion
      • it is the ion with the largest mass/charge ratio
      • there may be a smaller peak with a larger mass/charge ratio, but this is caused by isotopes and is not actually the molecular ion
    • fragments of molecules can be used to identify compounds -> show different functional groups and bonds
      • fragmentation is more likely to occur at weaker bonds so a stronger bond will have a greater abundance
    • carbonyl compounds generally fragment at the carbonyl group to form RCO+ (an acylium ion) and R-
      • acylium ions are stable as the positive charge is localised
      • a peak in the spectrum with one unit less than main peaks may show a loss of a H atom
    • molecules containing isotopes produce more than one molecular ion
      • Cl-35 is 3 times as abundant as Cl-37. Br-79 has the same abundance as Br-81.

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