acetate counterion is why your 10mg vial has 8.7mg of peptide
Posting this as a discussion rather than a claim: acetate counterion is why your 10mg vial has 8.7mg of peptide. Numbers, in the order they matter: 10mg and 8.7mg. UV at 214nm sees the peptide bond and picks up almost everything; at 280nm you are looking at aromatics only. Which wavelength the number came from is…
Area percent is the peak area of your compound over the total integrated area, at one wavelength, on one gradient. It is a relative measure of what the detector saw, not a mass fraction of the vial.
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Are the related substances itemised or is it a single total?
area% is not mass%, and the difference is the whole game
Is water content on the document? It changes your concentration arithmetic.
LC-MS gives you identity; UV purity gives you a relative quantity. A document with the first and not the second, or the reverse, is answering half the question.
The PDF creation date being later than the analysis date is usually a re-issue or a re-export. It is worth one question and it is not evidence of anything on its own.