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

•Canal rays produced different colors depending on the gas which produced them

Canal Rays

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)

Mass to Charge Ratio

Mass Spectrometer

•1905: Thomson Improved Instrument design. (Lower pressures improved resolution) R=13

•Observed mass spectra for polyatomic molecules

•Built the first mass spectrometer

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, CO2

2+, some new element.

Isotopes

CO

Ne

Isotopes

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.

Aston

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

Ionization of Metals

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?

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

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

Alfred Nier

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

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.

Manhattan Project

Manhattan Project

Installing Magnet Shims

Collecting Enriched Sample

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.

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

Resolution

•1913: R=13 (Thomson)

•1918: R=100 (Dempster)

•1937: R=2000 (Aston)

•1953: R=20,000 (Nier)

•1991: R=20,000,000 (Marshall)