AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
MFAssignR: Software Tools for Molecular Formula Assignment of Organic Aerosol
SIMEON SCHUM, Lynn Mazzoleni, Laura Brown, Michigan Technological University
Abstract Number: 562 Working Group: Instrumentation and Methods
Abstract Recently the use of ultrahigh resolution mass spectrometry has become increasingly popular in aerosol research due to its unparalleled ability to investigate the molecular composition of organic aerosol. Several methods have been developed to work with this data, including commercial (e.g., Composer, PetroOrg) and open source (e.g., Formularity, UltraMassExplorer) options. Open source methods are typically limited to molecular formula assignment based on a database matching approach. Meanwhile, commercial methods are typically capable of performing additional critical steps (e.g., noise estimation, isotope identification and mass recalibration), but they are often expensive and have little transparency regarding the molecular formula assignments. To address these deficits, we developed MFAssignR, an open source software package written in the R programming language available for download via GitHub. The MFAssignR package contains functions for molecular formula assignment, noise estimation, isotope identification, and mass recalibration. In MFAssignR, the molecular formula assignment is done in a data dependent way, meaning a priori decisions about the composition of a sample are not required to significantly decrease the overall assignment ambiguity. In addition, novel methods for noise estimation and isotope identification were developed as part of this package. From our comparison of MFAssignR to several other methods, we found that the MFAssignR assignments are equivalent for the higher intensity peaks and superior for the lower intensity peaks. This is due to the multiple molecular formula extensions used for assignment in MFAssignR. Furthermore, of the peaks commonly assigned, 97-99% were assigned to the same molecular formula. The development of MFAssignR is particularly valuable for organic aerosol research because previous methods, developed for either dissolved organic matter or petroleum samples, contained assumptions that are not appropriate for organic aerosol.