A Flexible Tool to Correct Superimposed Mass Isotopologue Distributions in GC-APCI-MS Flux Experiments

Abstract

The investigation of metabolic fluxes and metabolite distributions within cells by means of tracer molecules is a valuable tool to unravel the complexity of biological systems. Technological advances in mass spectrometry (MS) technology such as atmospheric pressure chemical ionization (APCI) coupled with high resolution (HR), not only allows for highly sensitive analyses but also broadens the usefulness of tracer-based experiments, as interesting signals can be annotated de novo when not yet present in a compound library. However, several effects in the APCI ion source, i.e., fragmentation and rearrangement, lead to superimposed mass isotopologue distributions (MID) within the mass spectra, which need to be corrected during data evaluation as they will impair enrichment calculation otherwise. Here, we present and evaluate a novel software tool to automatically perform such corrections. We discuss the different effects, explain the implemented algorithm, and show its application on several experimental datasets. This adjustable tool is available as an R package from CRAN.

Positional13C Enrichment Analysis of Aspartate by GC-MS to Determine PEPC ActivityIn Vivo

“…The comparably high deviation of fragment ion m/z 350, which is the [M+H] + adduct ion, originated from the presence of the molecular ion [M] + with overlapping MIDs. If no other fragment ions comprising the whole carbon backbone should be available, the E 13 C of m/z 350 could be corrected for the overlaid MID of m/z 349 using the previously reported correction function CorMID 43 .…”