Coming back to: Oxidation and deamidation mass shifts, tabulated

Oxidation and deamidation mass shifts, tabulated — setting out what I have, and where I think it stops being reliable.

Reading back through what has been written here about Oxidation and deamidation mass shifts, three questions come up every time and only one has ever been answered properly.

Listing all three, with what I think the state of the answer is for each, so the thread can start further along than the last one did.

The arithmetic in post #8 is right; the assumption feeding it is the part to check.

Sample preparation for mass spectrometry can itself introduce modifications, particularly oxidation. A finding at trace level may be telling you about the preparation rather than the material.

What mass accuracy establishes: the measured mass is consistent with a specific composition. What it does not establish: purity, sequence order, stereochemistry, or the absence of an isobaric species. Every one of those requires something else.

I have no interest in any supplier named above.

I read post #19 twice before replying, because I had assumed the opposite.

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.

This is the sort of thing the wiki should carry and currently does not.

Noted, and I have changed what I was going to do on the strength of it.

Narrowing post #30, because the general version has more than one answer.

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.

I would treat the number as indicative rather than as a measurement.