What does a Mass Spectrum say?
Mass spectrum of an antibody IgG.
A mass spectrum is the recording of a protein’s behavior - in this case, frequency around an electrode - within the mass spectrometer.
The mass information is encoded in terms of mass-to-charge ratio, or m/z. Each cluster of peaks, like the 25+, denotes a protein’s charge state - i.e., the number of protons charging the protein molecule. There is a distribution of charge states (from 22-28+) for the same set of molecules - this is why the fine pattern in each charge state looks the same but at different intensity.
Thus, the mass of the molecule (m) can be easily extracted from a system of equations that uses the m/z values for two different charge states (z).
The mass spectrum can also reveal multiple charge-state distributions. In this spectrum, there is a dominant distribution on the right. On the left, there are signs of at least two smaller distributions that correspond to the dissociated components of the molecular machine.
Mass Spectrum of the enzyme Alcohol Dehydrogenase
Mass Spectrum of Cesium Iodide Clusters
In another application, the mass spectrum can reflect the sizes of simple particles. This spectrum shows the distribution of masses that correspond to the formation and dissociation of Cesium Iodide salt clusters.