The history of mass spectrometry has its roots in physical and chemical studies regarding the nature of matter. The study of gas discharges in the mid 19th century led to the discovery of anode and cathode rays, which turned out to be positive ions and electrons. Improved capabilities in the separation of these positive ions enabled the discovery of stable isotopes of the elements. The first such discovery was with the element neon, which was shown by mass spectrometry to have at least two stable isotopes: 20Ne (neon with 10 protons and 10 neutrons) and 22Ne (neon with 10 protons and 12 neutrons). Mass spectrometers were used in the Manhattan Project for the separation of isotopes of uranium necessary to create the atomic bomb.
Prout's Hypothesis Prout's hypothesis was an early 19th-century attempt to explain the properties of the chemical elements using the internal structure of the atom. In 1815, the English chemist William Prout observed that the atomic weights that had been measured were integer multiples of the atomic weight of hydrogen. Prout's hypothesis remained influential in chemistry throughout the 1820s. However, more careful measurements of the atomic weights, such as those compiled by Jöns Jakob Berzelius in 1828 or Edward Turner in 1832, appeared to disprove it. In particular the atomic weight of chlorine, which is 35.45 times that of hydrogen, could not at the time be explained in terms of Prout's hypothesis. It would take the better part of a century for this problem to be resolved.
Canal rays
In the mid-nineteenth century, Julius Plücker investigated the light emitted in discharge tubes and the influence of magnetic fields on the glow. Later, in 1869, Johann Wilhelm Hittorf studied discharge tubes with energy rays extending from a negative electrode, the cathode. These rays produced a fluorescence when they hit a tube's glass walls, and when interrupted by a solid object they cast a shadow. Canal rays, also called anode rays, were observed by Eugen Goldstein, in 1886. Goldstein used a gas discharge tube which had a perforated cathode. The rays are produced in the holes (canals) in the cathode and travels in a direction opposite to the "cathode rays," which are streams of electrons. Goldstein called these positive rays "Kanalstrahlen" - canal rays.
Discovery of isotopes
In 1913, as part of his exploration into the composition of canal rays, J. J. Thomson channeled a stream of ionized neon through a magnetic and an electric field and measured its deflection by placing a photographic plate in its path. Thomson observed two patches of light on the photographic plate (see image on left), which suggested two different parabolas of deflection. Thomson concluded that the neon gas was composed of atoms of two different atomic masses (neon-20 and neon-22). Thomson's student Francis William Aston continued the research at the Cavendish Laboratory in Cambridge, building the first full functional mass spectrometer that was reported in 1919. He was able to identify isotopes of chlorine (35 and 37), bromine (79 and 81), and krypton (78, 80, 82, 83, 84 and 86), proving that these natural occurring elements are composed of a combination of isotopes. The use of electromagnetic focusing in mass spectrograph which rapidly allowed him to identify no fewer than 212 of the 287 naturally occurring isotopes. In 1921, F. W. Aston became a fellow of the Royal Society and received a Nobel Prize in Chemistry in the following year. His work on isotopes also led to his formulation of the Whole Number Rule which states that "the mass of the oxygen isotope being defined [as 16], all the other isotopes have masses that are very nearly whole numbers," a rule that was used extensively in the development of nuclear energy. The exact mass of many isotopes was measured leading to the result that hydrogen has a 1% higher mass than expected by the average mass of the other elements. Aston speculated about the subatomic energy and the use of it in 1936. In 1918, Arthur Jeffrey Dempster reported on his mass spectrometer and established the basic theory and design of mass spectrometers that is still used to this day. Dempster's research over his career centered around the mass spectrometer and its applications, leading in 1935 to his discovery of the uranium isotope 235U. This isotope's ability to cause a rapidly expanding fission nuclear chain reaction allowed the development of the atom bomb and nuclear power. In 1932, Kenneth Bainbridge developed a mass spectrometer with a resolving power of 600 and a relative precision of one part in 10,000. He used this instrument to verify the equivalence of mass and energy, E = mc2.
Manhattan Project
A Calutron is a sector mass spectrometer that was used for separating the isotopes of uranium developed by Ernest O. Lawrence during the Manhattan Project and was similar to the Cyclotron invented by Lawrence. Its name is a concatenation of Cal. U.-tron, in tribute to the University of California, Lawrence's institution and the contractor of the Los Alamos laboratory. They were implemented for industrial scale uranium enrichment at the Oak Ridge, Tennessee Y-12 plant established during the war and provided much of the uranium used for the "Little Boy" nuclear weapon, which was dropped onto Hiroshima in 1945.
Development of gas chromatography-mass spectrometry The use of a mass spectrometer as the detector in gas chromatography was developed during the 1950s by Roland Gohlke and Fred McLafferty. The development of affordable and miniaturized computers has helped in the simplification of the use of this instrument, as well as allowed great improvements in the time taken to analyze a sample.
Fourier transform mass spectrometry Fourier transform ion cyclotron resonance mass spectrometry was developed by Alan G. Marshall and Melvin B. Comisarow at the University of British Columbia in 1974. The inspiration was earlier developments in conventional ICR and Fourier Transform Nuclear Magnetic Resonance (FT-NMR) spectroscopy.
Soft ionization methods
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