Ion Composition Elucidation (ICE): an Investigative Tool for Characterization and Identification of Compounds of Regulatory Importance

Abstract

Ion composition elucidation (ICE) often leads to identification of compounds and provides high-quality evidence for tracking compounds to their sources. Mass spectra for most organic compounds are not found in mass spectral libraries used to tentatively identify analytes. In addition, multiple matches are common. Ion Composition Elucidation provides the numbers of atoms of each element in the ions in the mass spectrum, greatly limiting the number of possible compounds that could produce the mass spectrum. Review of chemical and commercial literature then limits the number of possible compounds to one or a few that can be purchased to confirm tentative compound identifications by comparison of mass spectra and chromatographic retention times. Ion composition elucidation is conceptually simple relative to other analytical techniques and more easily explained to a judge or jury. It is based on sums of the exact masses of atoms and their isotopic abundances. Several applications of ICE are demonstrated for ultra-trace-level compounds in an extract of the effluent from a tertiary sewage treatment plant including: (1) measurement of five values to determine an ion’s composition and to generate evidence for the compound’s identity, (2) rejection of incorrect library matches, (3) rapid screening for a target compound in an extract, and (4) a strategy for tracking unidentified compounds to their sources.