This is the second in a series on Isotope analysis using Orbitrap technology.
Multiply substituted isotopologues? It may sound complicated, but it’s remarkably simple and extremely useful. And even better, it’s easy to measure with the Thermo Scientific Orbitrap Exploris Isotope Solutions.
What is a multiply substituted isotopologue?
Take a molecule, e.g., CO2. The most common variety of CO2 is 12C16O16O. But in rare cases, the 12C could be replaced by a 13C and the 16O could be replaced by 17O or 18O. Where two or more of these isotopes have been swapped, this is called a multiply substituted isotopologue.
Why do we care about multiply substituted isotopologues?
Multiply substituted isotopologues give us important insights into the conditions and processes forming that molecule. For example, the carbonate multiple substituted isotopologue (13C18O16O, aka Δ47) has been widely used as a paleo-thermometer that is independent of variations in the oxygen isotopic composition of the source water. Similarly, multiply substituted isotopologues of methane have been used to identify the process of methane production in carbon capture and storage sites (e.g., Tyne et al. 2021). Multiply substituted isotopologues can provide important insights in biochemical applications, using isotope labeling to decipher metabolic pathways.
Why are multiply substituted isotopologues traditionally tricky to analyze?
Because of the difference in abundance between multiply substituted isotopologues and the major species, multiply substituted isotopologues have traditionally been tricky to measure. They require instrumentation that is sensitive enough to detect the minor isotope beams and also has the resolution to detect isobaric species, e.g., 13C18O16O from 12C18O17O.
What is game changing about the Orbitrap Exploris Isotope Solutions?
The Orbitrap Exploris Isotope Solutions has a mass resolution of up to 480,000 (at 200 m/z), allowing separation of isotopologues that are far beyond the reach of even the highest resolution magnetic sector mass spectrometer. What’s more, because it is possible to limit the mass range entering the analyzer, the major species can be excluded (so-called “noM0” methodology), allowing a greater number of counts on the multiply substituted isotopologues. This means that the sensitivity of Orbitrap Exploris Isotope Solutions is adaptable for your application and the multiply substituted isotopologues of interest.
For more information, visit: thermofisher.com/orbitrap-for-isotopes.
Bulk isotopic composition of multiply substituted isotopologues is just the tip of the iceberg in terms of the advantage of the Orbitrap Exploris Isotope Solutions. Read Part 3 of this series to find out about how this technology can be used to uncover site-specific isotope information.
Related blog posts in this three-part series
Part 1: Boost Your Productivity with the Isotopic Analysis of Intact Molecules
Part 3: New Dimensions in Isotope Ratio Analysis: Site Specificity