Recently, the use of ultrahigh resolution mass spectrometry has become increasingly popular for the analysis of organic aerosol and other complex organic matter samples due to its unparalleled ability to investigate the molecular composition of such samples. The richness and large amount of data generated in these studies requires access to advanced software tools to perform effective data preparation and molecular formula assignment. This led us to develop MFAssignR, an open-source software package written in the R programming language and available on GitHub. MFAssignR includes functions for molecular formula assignment, noise estimation, isotope filtration, and mass recalibration. These functions give MFAssignR the ability to act as a self-contained pipeline for the preparation and analysis of ultrahigh resolution mass spectrometry data. Molecular formula assignment in MFAssignR is based on the CHOFIT algorithm and a novel implementation of formula extension, that relies on the interconnectedness of complex organic matter to create data-dependent pathways for reducing formula ambiguity and the need for a priori decisions. The potential for ambiguous molecular formulas (more than one formula per mass) was a driving force in developing this code and the ability to report ambiguous formulas is retained, separating MFAssignR from many other molecular formula assignment software. Additionally, the idea of formula extension using one or more subunits common in complex organic matter (CH₂, H₂O, H₂, CH₂O, O) was used to develop novel implementations of the other functions (noise estimation, isotope filtration, and mass recalibration) in MFAssignR. Many researchers have begun to implement MFAssignR in their research leading to multiple published works. This presentation will seek to familiarize you with MFAssignR and how you may be able to use it in your own work.

Simeon Schum

Michigan Technological University

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