Massive cluster ions of CsI (mass-to-charge ratio > 25,000) have been produced, mass analyzed, and detected with a conventional double-focusing mass spectrometer. Variations in the ion intensity distributions depend on the relative lifetime of the ions. These results are of fundamental interest, but they also impact the practical limits of mass spectrometry.
Joseph E. Campana, Richard J. Colton, Jeffrey R. Wyatt, Robert H. Bateman, and Brian N. Green, "Ultra-high Mass Spectrometry," Appl. Spectrosc. 38, 430-432 (1984)