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Mass Spectrometry: Origins

Mass Spectrometry: Origins. 11/1/2006. Canal Rays. 1886: Goldstein discovers “canal rays” Traveled in the opposite direction in vacuum tubes compared to cathode rays Unlike cathode rays, weak magnetic fields did not affect canal rays

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Mass Spectrometry: Origins

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  1. Mass Spectrometry:Origins • 11/1/2006

  2. Canal Rays • 1886: Goldstein discovers “canal rays” • Traveled in the opposite direction in vacuum tubes compared to cathode rays • Unlike cathode rays, weak magnetic fields did not affect canal rays • Canal rays produced different colors depending on the gas which produced them

  3. Canal Rays

  4. Mass to Charge Ratio • 1898: Wien showed that canal rays could be deflected with strong magnetic and electric fields. • Parallel electric and magnetic fields caused the rays to travel in parabolic paths • Particles of different m/z followed different curves. (Different gases gave different m/z)

  5. Mass to Charge Ratio

  6. Mass Spectrometer • 1905: Thomson Improved Instrument design. (Lower pressures improved resolution) R=13 • Observed mass spectra for polyatomic molecules • Built the first mass spectrometer

  7. Isotopes • Elements were thought to be made of atoms of a single mass. • Neon gave rise to two lines in the mass spectrometer at m/z 20 and 22. • Thomson gave explanations like NeH2, CO22+, some new element.

  8. Isotopes Ne CO

  9. Isotopes

  10. Isotopes • Isotopes were thought to only exist in the case of radioactive elements. • Aston Improved instrument design R=130. • 1919: Aston extended the concept of isotopes to stable elements. • By 1924 isotopic masses and abundances for 53 elements had been measured.

  11. Aston

  12. Ionization of Metals • 1935: Arthur Dempster developed an ion source that allowed ionization of solid metals. • Several groups worked to complete isotopic analysis of nearly every element in the periodic table by the mid 1930’s

  13. Ionization of Metals

  14. Non Integer Masses • Isotopes were thought to have whole number masses. • 1937: Aston improved instrument design to achieve R=2000. • Discovered that isotopic masses are not whole number multiples of hydrogen. • How can this “Missing Mass” be explained?

  15. Non Integer Masses • K.T. Bainbridge Proves Einstein’s theory of mass-energy equivalence in 1932 • E=mc2 • Mass defects arise from differences in nuclear binding energy

  16. Alfred Nier • 1937: Nier improved design to perform precise nuclear mass measurements. 13C/12C ratio varies depending on the source in nature. • 1939: Nier develops a more compact, inexpensive design allowing 13C analysis to trace metabolism. • 1939: Measured 238U/235U ratio of 139/1. • 1953: Developed double focusing instrument

  17. Alfred Nier

  18. Manhattan Project • 1940: Fermi and Dunning Prompted Nier to use his instrument to collect pure 235U. • Nier collected nanograms of 235U, and neutron bombardment showed it was fissionable. • 1942: E.O. Lawrence modified his cyclotron to collect 100 micrograms of pure 235U

  19. Manhattan Project • 1943: Many large mass spectrometers were built at Oak Ridge to scale up production. • 1945: Hundreds of such instruments operate simultaneously to produce 200 grams of 80% enriched 235U on a daily basis.

  20. Manhattan Project

  21. Manhattan Project Installing Magnet Shims Collecting Enriched Sample

  22. Manhattan Project • 1944: Gaseous diffusion was also used to purify uranium. • Nier-type mass spectrometers, mass-produced by GE, were used as leak detectors in the construction of the plant. • 100 Nier mass spectrometers were used for continuous monitoring of the process.

  23. Summary of MS Applications by 1945 • General-Purpose analytical tool for mixture analysis and quantitation • Preparative isotope separation • Process stream monitoring • Leak detection in vacuum systems

  24. Resolution • 1913: R=13 (Thomson) • 1918: R=100 (Dempster) • 1937: R=2000 (Aston) • 1953: R=20,000 (Nier) • 1991: R=20,000,000 (Marshall)

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