Mass spectrometry in the mid-1930’s: were chemists intrigued?

The direct demonstration of the existence of isotopes, the highly precise measurements of atomic masses, and the determinations of appearance potentials for gaseous ions generated by electron impact, that were reported during the interval 1920–1935, had their origin in earlier investigations of electrical discharges in gases at modest pressures that were initiated late in the 19th century. J. J. Thomson’s studies of rays of negatively- and positively-charged particles led to his characterization of the former as electrons and the latter as atomic/molecular fragments that he identified via the first mass spectrometer. In the following survey I traced the evolution of mass spectrometry and the role it played in the direct demonstration of the isotopic composition of the elements. While its potential utility as an analytical tool was recognized by J. J. Thomson, its practical application had to await the development of ancillary laboratory techniques. With respect to investigations of isotopes, complementary but distinct routes were followed by physicists and chemists during the two decades after WWI. The last section of this report recounts my personal experiences with mass spectrometry and with several of the principal personae during the years 1930–1935.