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Training & Protocols

Tutorial for Interpreting General Mass Spectra

Information Obtained From a Mass Spectrum

  1. Ion Identification: The spectrometer can identify ions based upon their ratio of mass to charge (or m/z ratio).
  2. Fragmentation of Ions: In the process of creating gas phase ions, the whole, intact molecule (parent) may fragment into a variety of smaller pieces. These fragments can also be charged and thus be detected at a different mass to charge ratio than their parental precursor.
  3. Structure of Parent: The total pattern of ions detected in a mass spectrum can reveal information about the composition and structure of the parent molecule.

A Simple Example- Water (H2O)

Spectrum of Water

The mass spectrum of water would be similar to the spectrum above. Each peak of the spectrum represents the m/z of a unique ionic species.

To illustrate this, compare the spectrum with the following information:

  • m/z =18 (H20)+ since O + H + H = 16 + 1 + 1 = 18 amu
  • m/z=17 (HO)+ since O + H = 16 + 1 = 17 amu
  • m/z=16 (O)+ since O = 16 amu
  • m/z=1 (H)+ since H = 1 amu

Steps for Revealing Mass Spectral Information

Some general ways to reveal information in a mass spectrum include:

  1. Determine the exact mass of a peak to reveal its elemental composition.
  2. Assign the heaviest m/z as the parent molecule.
  3. Check for isotopic abundances in a greater magnification of the peak to reveal the presence of isotopic elements.
  4. Record the fragmentation pattern to "fingerprint" the molecule and to reveal details of its structure.

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