[DoctorDomo]

I was looking through mass spec interpretation examples, and I saw one with an M+3 peak. All the isotopic abundance tables I've seen show M+1 and M+2 peaks, first time I've seen M+3. Is this a rare thing to have an M+3 isotope in reasonable abundance? What are the main elements which have common M+3 isotopes?

[DoctorDomo]

I see that bromine has two naturally occuring isotopes of near equal abundance, so when you look for the molecular ion on a spectrum containing bromine, you see something like this:

at the end of the spectrum. Which peak is the molecular ion? Is it the one containing the isotope with the lowest atomic mass?

Side question: What is the small peak at the very end of the spectrum? What could cause this M+3 peak? Heres the compound for this mass spectrum:

Br and N don't have any isotopes that could make that peak. Could it be due to a molecule containing both ⁸¹Br and ¹⁵N? Yeah that makes sense, if both of those bromine isotopes are equally abundant, then your gonna get equal amounts of each compound and its ¹⁵N isotope.

[DoctorDomo]

EDIT: I posted this before seeing that my threads were merged so I probably didn't say anything new in this reply.

I figured it out. Its something you probably only see in spectra with a bromine atom. Since bromines common isotopes occur in a near 50:50 ratio, whatever smaller peak you see beside the molecular ion peak, you'll see the same thing beside the ⁸¹Br peak.