U.S. Environmental Protection Agency


Date of this Version



Published in Liquid Chromatography Time-of-Flight Mass Spectrometry: Principles, Tools, and Applications for Accurate Mass Analysis (2009) 35-56.


Exact masses of ions and relative isotopic abundances (RIAs) of the +1 and +2 isotopic mass peaks, measured with sufficient accuracy, provide the elemental compositions of ions and limit the number of possible compound identities. Double focusing mass spectrometers provided both exact mass and RIA measurements in the early 1990s, while today, less expensive, more robust, and easier to operate time - of - flight mass spectrometers (TOFMSs) provide data sufficiently accurate to determine ion compositions. Using exact masses and RIAs measured with a TOFMS, an Ion Correlation Program matches precursor ion and product ion:neutral loss pairs to increase the mass range for which the unique and correct composition of ions can be determined and to provide deconvolution of composite mass spectra. This chapter briefly reviews the evolution in the types of mass spectrometers, data acquisitions, and automated determination of ion compositions used in our laboratory to more easily and rapidly identify compounds.