There are many different types of MS detectors, but they all operate according to the same basic process:
- The MS ionizes the sample
- The MS separates the ions according to their mass
- The separated ions move toward a detector where they are counted
The data system compiles a spectrum showing the mass distribution of the ions produced from the sample—a snapshot of ion intensities plotted against their mass-to-charge ratios (m/z).
NOTE
In the majority of cases, z=1 and the x axis becomes equivalent to the ion mass, m.
A full structural analysis generally relies on the presence of a molecular ion and the measurement of the monoisotopic mass of the compound. Ionization initially produces molecular ions, but complex secondary processes can cause the molecular ions to fragment. Together with molecular ions, these fragment ions make up the mass spectrum. For individual chemical substances, a mass spectrum can be a characteristic molecular fingerprint.
The following topics detail different features of mass spectra: