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Small Molecule Isotope Resolved Formula Enumeration: a Methodology for Assigning Isotopologues and Metabolites in Fourier Transform Mass Spectra

preprint
revised on 28.05.2019 and posted on 28.05.2019 by Hunter Moseley, Joshua Mitchell, Robert M Flight
Improvements in Fourier Transform Mass Spectrometry (FT-MS) enable increasingly more complex experiments in the field of metabolomics. What is directly detected in FT-MS spectra are spectral features (peaks) that correspond to sets of adducted and charged forms of specific molecules in the sample. The robust assignment of these features is an essential step for MS-based metabolomics experiments, but the sheer complexity of what is detected and a variety of analytically-introduced variance, errors, and artifacts has hindered the systematic analysis of complex patterns of observed peaks with respect to isotope content. We have devel-oped a method called SMIRFE that detects small biomolecules and determines their elemental molecular formula (EMF) using de-tected sets of isotopologue peaks sharing the same EMF. SMIRFE does not use a database of known metabolite formulas, instead a nearly comprehensive search space of all isotopologues within a mass range is constructed and used for assignment. This search space can be tailored for different isotope labeling patterns expected in different stable isotope tracing experiments. Using consumer-level computing equipment, a large search space of 2000 daltons was constructed and assignment performance was evaluated and validated using verified assignments on a pair of peak lists derived from spectra containing unlabeled and 15N-labeled versions of amino acids derivatized using ethylchloroformate. SMIRFE identified 18 of 18 predicted derivatized EMFs and each assignment was evaluated statistically and assigned an e-value representing the probability to occur by chance.

Funding

NSF 1419282 and NSF ACI1626364

History

Email Address of Submitting Author

hunter.moseley@uky.edu

Institution

University of Kentucky

Country

United States of America

ORCID For Submitting Author

0000-0003-3995-5368

Declaration of Conflict of Interest

No conflicts to declare.

Version Notes

Version 3.9

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