Oxidation and deamidation mass shifts, tabulated

Resolution and mass accuracy are different specifications. An instrument can resolve two species and still assign their masses imprecisely, and the reverse is also possible.

Happy to be corrected if someone holds better data than mine.

Answering the question post #13 raises rather than the one it answers.

The honest summary of what a mass result buys you: it narrows the field of what the material could be, considerably. It never closes it, and no certificate should be read as though it had.

That is one dataset and I would not build a rule on it.

Understood. Thank you for being specific about the limits of it.

Where I part company with post #32, and it is a narrow parting.

Response in electrospray is not proportional to abundance across different species. Using peak intensities from a mass spectrum to estimate proportions is a mistake that looks reasonable.

Mass error in parts per million is (observed minus theoretical) divided by theoretical, times a million. On a high-resolution instrument a low single-digit figure is unremarkable and expected.

Take it as a starting point and not as a specification.

Tandem mass spectrometry with fragmentation gives sequence information that intact mass cannot. It is the analysis that would actually confirm identity, and it is rarely supplied.

I keep a log of this specifically because memory is unreliable about it.

Monoisotopic and average mass are different numbers and both appear on documents. At this molecular weight the difference is a few daltons, which is more than the tolerance being claimed.

Not disagreeing with anyone above, just adding the bit I keep having to look up.

Post #69 answers the question as asked. The question underneath it is different.

I changed my mind about oxidation and deamidation mass shifts after someone here asked me for the source and I could not produce one. That is worth saying out loud because it is the ordinary way it happens.