A mass spectrometer is a device designed to separate ions and record their intensities. A typical mass spectrometer is comprised of three parts: an ion source, a mass analyzer, and a detector.
The ion source subjects a sample of material with an electrical charge that causes the material to emit ionozed particles. These particles are then moved as a gas to the seperator or mass analyzer. Types of ion sources include electrospray ionization and matrix-assisted laser desorption ionization.
The mass analyzer is the most flexible part of the mass spectrometer. Since an electric field will deflect charged particles, and the energy potential can be converted to inertial movement based on the mass and the potential, the mass analyzer uses these facts to steer certain masses to the detector based on their mass-over-charge ratios (m/z) by varying the electrical field potentials. It can be used to stabilize a narrow range of m/z or to scan through a range of m/z to catalog the ions present. Several types exist, include time-of-flight, ion trap, and quadrupole mass analyzers.
The detector simply records the charge induced when an ion passes by or hits a surface. If a scan is conducted in the mass analyzer, the charge induced in the detector during the course of the scan will produce a mass spectrum, a record of the m/z's at which ions are present.
A tandem mass spectrometer is one that is capable of multiple rounds of mass spectrometry. For example, one mass analyzer can isolate one peptide from many entering a mass spectrometer. A second mass analyzer then stabilizes the peptide ions while gas collides with them, causing them to fragment. A third mass analyzer then catalogs the fragments produced from the peptides. This process, called collision induced dissociation, is the basis of many experiments in proteomics.