Named, unnamed and unspecified impurities as regulatory categories

On the subject in the title: Named, unnamed and unspecified impurities as regulatory categories Working notes rather than a conclusion.

Working through the identity arithmetic and I would like it checked.

retatrutide has a monoisotopic mass close to 4731.3 Da. On an electrospray instrument I would expect to see the multiply charged series rather than the intact singly charged ion, so for the doubly charged species I calculate (4731.3 + 2 x 1.00728) / 2, and for the triply charged the analogous expression.

The observed values in the report sit within a few ppm of those. My question is what that actually establishes, because I have seen people treat a mass match as a purity result and I do not think it is one.

Deamidation at asparagine and glutamine: adds 1 approximately. Frequently appears as a close-eluting pair. It is a chemical modification that occurs during storage.

For anyone arriving from a search: the marked solution above is the direct answer, and the replies underneath it add the caveats that make it safe to use.

Coming back to post #8, because the follow-up matters more than the original answer.

Acetate content: counter-ion content. Trifluoroacetate or acetate from the salt form of the peptide. Affects mass calculations and should be stated on a complete certificate.

Coming back to post #11, because the follow-up matters more than the original answer.

Disulfide formation: if a peptide contains cysteine, it can form disulfide bonds with itself or with other molecules. Under oxidising conditions multiple species appear. Reducing conditions (like DTT) convert them back.