Training & Protocols
Tutorial for Interpreting General Mass Spectra
- Information Obtained From a Mass Spectrum
- Tutorial Using Water as an Example
- Steps for Revealing Mass Spectral Information
Information Obtained From a Mass Spectrum
- Ion Identification: The spectrometer can identify ions based upon their ratio of mass to charge (or m/z ratio).
- 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.
- 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)
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:
- Determine the exact mass of a peak to reveal its elemental composition.
- Assign the heaviest m/z as the parent molecule.
- Check for isotopic abundances in a greater magnification of the peak to reveal the presence of isotopic elements.
- Record the fragmentation pattern to "fingerprint" the molecule and to reveal details of its structure.
