Mass spectrometry
Technique measuring ion mass-to-charge ratios for chemical analysis.
Mass spectrometry (MS) is an analytical technique that measures the mass-to-charge ratio of ions, presenting the results as a mass spectrum—a plot of signal intensity against this ratio. This spectrum is used to determine a sample's elemental or isotopic signature, the masses of particles and molecules, and to elucidate chemical identity or structure. The technique is applied across many fields to both pure samples and complex mixtures.
In a typical procedure, a solid, liquid, or gaseous sample is ionized, often by bombardment with a beam of electrons. This can cause molecules to fragment into positively charged pieces or become positively charged without breaking apart. These ions are then separated by their mass-to-charge ratio, commonly by accelerating them through electric or magnetic fields, which deflect ions of the same ratio equally. A detector, such as an electron multiplier, captures the charged particles, and the resulting data is displayed as a spectrum. Identification of atoms or molecules is achieved by correlating known masses or characteristic fragmentation patterns.
The history of MS began in 1886 when Eugen Goldstein observed positively charged "canal rays" moving away from the anode in gas discharges. Wilhelm Wien later used perpendicular electric and magnetic fields to separate these rays by charge-to-mass ratio, and J. J. Thomson improved the device by reducing pressure, creating the mass spectrograph. Early instruments recorded spectra on photographic plates or used phosphor screens. Modern techniques were devised by Arthur Jeffrey Dempster and F.W. Aston in 1918 and 1919. Sector mass spectrometers called calutrons, developed by Ernest O. Lawrence, were used for uranium enrichment during the Manhattan Project. Later innovations included the ion trap technique, recognized with a Nobel Prize in Physics in 1989, and electrospray ionization and soft laser desorption, which earned a Nobel Prize in Chemistry in 2002 for their application to biological macromolecules.
A mass spectrometer comprises five components: a sample inlet, an ion source, a mass analyzer, a detector, and a data system. The inlet prepares the sample; the ion source converts a portion into a stream of ions; the mass analyzer separates ions by mass-to-charge ratio; and the detector measures abundances, sometimes providing spatial information. This modular design allows g
- field
- Analytical chemistry, physics
- known_for
- Measuring mass-to-charge ratio of ions; identifying chemical composition and isotopic ratios
- key_inventors
- Eugen Goldstein, Wilhelm Wien, J. J. Thomson, Arthur Jeffrey Dempster, F.W. Aston, Ernest O. Lawrence
Lore & Background
Mass spectrometry is an analytical technique used to determine the mass-to-charge ratio of ions. The results are presented as a mass spectrum, a plot of intensity versus mass-to-charge ratio, which is used to identify the elemental or isotopic composition of a sample, the masses of particles and molecules, and the chemical structure of compounds. The technique is applied across many fields to both pure samples and complex mixtures. In a typical procedure, a solid, liquid, or gaseous sample is ionized, often by bombardment with a beam of electrons, which can cause molecules to break into positively charged fragments or become positively charged without fragmenting. These ions are then separated by their mass-to-charge ratio, for example by accelerating them through electric or magnetic fields, where ions of the same ratio undergo the same deflection. Detected by a mechanism such as an electron multiplier, the ions produce a spectrum of signal intensity versus mass-to-charge ratio. Atoms or molecules are identified by correlating known masses or characteristic fragmentation patterns. The instrument comprises five components: a sample inlet, an ion source, a mass analyzer, a detector, and a data system. The ion source converts a portion of the sample into a stream of ions, which is then separated by the mass analyzer according to mass-to-charge ratio. The detector measures the abundance of each ion, and some detectors also provide spatial information.
Reader's Guide
Mass spectrometry is a foundational analytical technique with broad significance. It allows identification of elements, isotopes, and molecular structures by measuring mass-to-charge ratios of ions. Its development spans over a century, from Goldstein's canal rays to modern ionization methods enabling analysis of large biomolecules like proteins. The technique's flexibility is evident in its five components—sample inlet, ion source, mass analyzer, detector, and data system—each independently variable. Applications range from pure samples to complex mixtures, including coupling with gas chromatography (GC-MS) or liquid chromatography (HPLC-MS). The calutron's role in uranium enrichment during the Manhattan Project highlights its historical impact. Nobel prizes awarded for ion trap and soft ionization techniques underscore its ongoing evolution. Mass spectrometry remains essential in chemistry, physics, biology, and medicine for precise compositional and structural analysis.
Did You Know?
- The term 'mass spectrograph' was used for early devices recording mass spectra on photographic plates.
- Calutron mass spectrometers were developed by Ernest O. Lawrence for uranium isotope separation during the Manhattan Project.
- Half of the 1989 Nobel Prize in Physics was awarded for the development of the ion trap technique in the 1950s and 1960s.
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