Metabolite Spectral Accuracy on Orbitraps.

TitleMetabolite Spectral Accuracy on Orbitraps.
Publication TypeJournal Article
Year of Publication2017
AuthorsSu, X, Lu, W, Rabinowitz, JD
JournalAnal Chem
Volume89
Issue11
Pagination5940-5948
Date Published2017 06 06
ISSN1520-6882
KeywordsAlgorithms, Isotope Labeling, Isotopes, Mass Spectrometry, Metabolomics, Molecular Weight
Abstract

Orbitraps are high-resolution ion-trap mass spectrometers that are widely used in metabolomics. While the mass accuracy and resolving power of orbitraps have been extensively documented, their spectral accuracy, i.e., accuracy in measuring the abundances of isotopic peaks, remains less studied. In analyzing spectra of unlabeled metabolites, we discovered a systematic under representation of heavier natural isotopic species, especially for high molecular weight metabolites (∼20% under-measurement of [M + 1]/[M + 0] ratio at m/z 600). We hypothesize that these discrepancies arise for metabolites far from the lower limit of the mass scan range, due to the weaker containment in the C-trap that results in suboptimal trajectories inside the Orbitrap analyzer. Consistent with this, spectral fidelity was restored by dividing the mass scan range (initially 75 m/z to 1000 m/z) into two scan events, one for lower molecular weight and the other for higher molecular weight metabolites. Having thus obtained accurate mass spectra at high resolution, we found that natural isotope correction for high-resolution labeling data requires more sophisticated algorithms than typically employed: the correction algorithm must take into account whether isotopologues with the same nominal mass are resolved. We present an algorithm and associated open-source code, named AccuCor, for this purpose. Together, these improvements in instrument parameters and natural isotope correction enable more accurate measurement of metabolite labeling and thus metabolic flux.

DOI10.1021/acs.analchem.7b00396
Alternate JournalAnal. Chem.
PubMed ID28471646
PubMed Central IDPMC5748891
Grant ListP30 DK019525 / DK / NIDDK NIH HHS / United States
R01 CA163591 / CA / NCI NIH HHS / United States
R50 CA211437 / CA / NCI NIH HHS / United States