Holy cow. I'm just going to leave this here until I have time to come back to this. If you're solely doing shotgun proteomics by LCMS this might not be the most interesting thing you've ever seen.
If you're from time to time digging all the way into your data to determine the difference between a PNGase cleaved glycopeptide or a citrullination and a C13 isotope or 4, or you've wondered things like:
"why can't I use isotopic distributions at 700,000 resolution to determine if this is really pomegranate juice because of the different carbon fixation mechanisms used by different plants" (hint, it still isn't pomegranate juice, global production is still only a small fraction of global consumption)
or attempted to use isotope shifts to determine how old the material is in a drilled core geological sample is
or tried to distinguish between natural and synthetic compounds
You've probably been extremely annoyed about the inability to calibrate your isotopic distribution and maybe thought of crazy ways to do it yourself and then given up.
If any of this applies to you: