Tutorial for Interpreting General Mass Spectra
- Information Obtained From a Mass Spectrum
- Tutorial Using Water as an Example
- Steps for Revealing Mass Spectral Information
- Tutorial Using Methyl Chloride to Show Isotopic Influence
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.
Tutorial Using Methyl Chloride to Show Isotopic Influence
Go to the EMSL website for the Tutorial Using Methyl Chloride to Show Isotopic Influence.
