Structural identification of reagent anions frequently used in mass-spectrometric analyses

Ion/ion reactions are an analytically useful set of chemical reactions, providing means for probing and manipulating analyte ions in mass spectrometry. In recent years, peptide fragmentation techniques employing gas phase ion/ion reactions have emerged as promising tools in the vast array of ion activation methods available. Particularly, electron transfer dissociation (ETD) tandem mass spectrometry (MS/MS) is now a method of choice, enabling both top-down proteomics and the characterization of post-translational modifications.

Fluoranthene (MW 202) is one of the most widely used reagent ions for both ETD and proton transfer reactions (PTR), as reagent ions for both reactions can be generated by the same neutral precursor. These reagents are easily generated by electron attachment for ETD (radical anion m/z 202), or hydrogen (H) atom attachment to the radical anion for PTR (closed-shell anion m/z 203) in a chemical ionization source.

Jonathan Martens and his colleagues at the FELIX Laboratory have used infrared ion spectroscopy in combination with density functional theory calculations to identify the structures of these reagent anions. They establish that the m/z 203 PTR reagent anion possesses a structure that deviates from what has been suggested previously and provides insight into the reaction mechanism involved in PTR. This conclusion may lead to further insights into PTR reactions, which are utilized on many mass spectrometry platforms, and forms a fundamental understand of these processes that can assist future developments.

Publication
Structures of Fluoranthene Reagent Anions Used in Electron Transfer Dissociation and Proton Transfer Reaction Tandem Mass Spectrometry
Jonathan Martens, Giel Berden, and Jos Oomens
Analytical Chemistry, May 2016
DOI: 10.1021/acs.analchem.6b01483