The figure shows a spectrum of ethylacetate (MW=88) for 70-eV electrons. Usually for GC/MS analysis, a 70eV electron is used for ionization. A reason to use this energy is that the mass spectra in many libraries, which are frequently used for identification of unknown sample peaks, are customarily measured with 70-eV electrons. When the electron energy is changed, the spectrum changes as per the following:

  • Ion signal is most intense at around 70eV.
  • When the energy is decreased, the spectrum will be less fragmented and the signal intensity seriously decreases. Ions cannot be produced below about 10eV.

LICK"14eV" ("70eV") 

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