An APP for untargeted feature extraction from isotope dilution metabolomics data.
An emzed2 application for LC-MS data acquired with Orbitrap high mass resolution instruments.
The application allows untargeted extraction of metabolites based on isotope dilution mass spectrometry (IDMS) method. For each metabolite a pair of an natural labeled [12C] and an uniformly 13C labeled [13C] isotopologue is present in the same sample, since the sample is a mixture of respective cell extracts. As unlabeled and labeled isotopologues have the same physicochemical properties, the corresponding LC-MS peaks will co-elute and the m/z difference equals
n* (mz.C13 - mz.C12)*z
where n corresponds to the number of the metabolite carbon atoms, mz.c12 is the m/z of the 12C isotope, mz.C13 equals the m/z of the correpsonding 13C isotope, and z is the charge state of the ions. In addition, untargeted metabolite extraction is not only based on analysis of an IDMS sample, but also on individual LC-MS measurements of the corresponding [12C] and the [13C] extracts, respectively. Separate analysis allows direct assignment of isotopologue identity ([12C], [13C]) in the IDMS sample. Overall, this approach significantly reduces the number of false positive metabolites and enhances metabolite annotation as the number carbon atoms can be determined from the isotopologue mass distances.
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