Advancing Patient Care Through Research
Washington University School of Medicine

History of Mass Spectrometry

Obviously, mass spectrometers did not exist in 1907. But the basic physics underlying the development of the mass spectrometer was being researched intensely during this period, primarily in Europe and the United Kingdom. In the previous year, J. J. Thompson was awarded the Nobel Prize in Physics “in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases”. Click to go directly to his page on Today, we think of this accomplishment as the discovery of the electron.

An important paper by Thomson on his research on the electron was published almost a decade earlier in Philosophical Magazine1. Thomson’s approach to the problem of teasing out the properties of the electron, or corpuscle of negative electricity is summarized in the abstract of that publication below.

It has been conclusively shown that the charge on an ion produced in a gas by the action of cathode rays is the same as the charge carried by the hydrogen ion in electrolysis. It is shown in the present paper that the ratio of the mass of the ion to the charge. m/e, for negative electrification, in the case of the action of ultra-violet light on a rarefied gas or the electrification produced by an incandescent carbon filament is the same as the ratio for cathode rays. This ratio is of the order of 6.8 * 10-6, while the same ratio for electrolysis is of the order to 4. It follows that the charge e being the same, that the mass, m, of the negative ion in a gas must be about the one thousandth part of a hydrogen atom. The positive ion is, on the contrary, of the same relative size as the atom, as is shown by the ratio of m/e being the same as in ordinary electrolysis. The author considers from the general results that the negative ion must be of fundamental importance in any theory of electrical action, and considers that it may be the fundamental quantity in terms of which all electrical quantities may be expressed. He considers that the gaseous atom may consist of a large number of corpuscles which are equal to each other and that the mass of one of these corpuscles is the same as the negative ion in a gas at low pressures, or about 3×10-26 of a gramme. When electrified, one corpuscle splits off from the aggregation to form the negative ion and leaves the positive ion of greater mass. Electrification would then depend on the splitting up of the atom itself.

1) Thomson, J. J. (1899). “On the masses of the ions in gases at low pressures.” Philosophical Magazine (1798-1977) 48: 547.

A video of Thomson discussing his work was recorded on film in 1934 and can be viewed at the site.

The apparatus that Thomson used in the discovery of the electron is shown in the picture below.

Thomson Apparatus Electron Discovery
(Photo Courtesy of the Cavendish Lab, Cambridge UK)

A gas discharge was initiated in the small bulb to the left which was filled with an appropriate gas. Negative ‘corpuscles’ were accelerated from the cathode to the anode and through the slit ‘S’. Magnetic and/or electric fields could be placed in the region shown, thus permitting the study of the negative corpuscles of electricity.

Thomson's Aapparatus