Gas chromatography-mass spectrometry (GC-MS) is a valuable analytical tool that is used by numerous scientific fields including forensics, medicine, environmental monitoring, and petrochemicals. Until recently, many GC-MS instruments have relied on either electron ionization or chemical ionization sources. While these sources provide means to identifiy chemical species, their ability to do so can be limited by the quality of the mass analyzer, i.e. mass accuracy. In response to this need, Thermo Fisher Scientific launched the Q Exactive™ GC hybrid quadrupole-Orbitrap MS utilizing these sources, while other companies, such as Waters Corp, Bruker, and Agilent, have also released GC-MS systems capable of exact mass measurements; however, these GC-MSs employ a different ionization source: atmospheric pressure chemical ionization (APCI). APCI, like other atmospheric pressure ionizations (API), provides “soft” ionization of analytes which, when combined with high-resolution mass spectrometry, provides reasonable unknown identification by exact mass. Previously, an interface between a GC and Orbitrap MS, that allows users to easily switch between GC and liquid chromatography separations and utilizes APCI, was described. Using this GC-APCI interface, several analyses were conducted measuring analytes of decreasing polarities. Although the interface produced [M + H] ions, it also generated unique species for less polar molecules. These species were also detected using an atmospheric pressure photoionization source. Specifically, [M – 32.0267] and [M – 45.0347] ions from fatty acid methyl esters (FAMES) as well as [M + 12.9710] and [M + 28.9657] ions from alkanes were generated consistently. When analyzing complex mixtures of unknown composition, the ability to accurately predict how known analytes will ionize is of the utmost importance. This presentation reports investigations undertaken to elucidate the ionization mechanisms of these compounds via atmospheric pressure ionizations. In particular, high-resolution and MS<sup>2</sup> data were collected using a Q Exactive™ Orbitrap for fully deuterated analytes from both chemical classes. It was found that alkanes were readily oxidized to ketones and specific FAMEs underwent a similar process following in-source fragmentation. From these experiments, the data suggest unique, underreported mechanisms of API.

Investigation of atmospheric pressure ionization of alkanes and fatty acid methyl esters

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.