(August 2004) Development of mass spectrometry began with J.J. Thomson’s vacuum tube, with which, in the early part of the 20th century, he demonstrated the existence of electrons and “positive rays.” Thomson observed that the new technique could also be used by chemists to analyze chemicals. Despite this far-sighted observation, the primary application of mass spectrometry remained in the realm of physics for nearly thirty years. It was used to discover a number of isotopes, to determine the relative abundance of isotopes, and to measure isotope masses. These important fundamental measurements laid the foundation for later developments in diverse fields…