Storage-related degradation and synthesis-related impurity look different on a chromatogram. A growing oxidation peak over time is not a manufacturing finding.
Asking directly, because I could not find a straight answer: Attributing a new peak: degradation product or excipient?
A narrow question about attributing a new peak, deliberately narrow, because the broad version has been asked here four times and produced four long threads and no answer.
One question, stated units, stated method, and what I have already ruled out.
This follows post #2 rather than contradicting it.
Deamidation at asparagine or glutamine adds approximately one dalton and frequently produces a close-eluting pair. It is the impurity most likely to be integrated into the main peak by accident.
It is one reading of the data and not the only reasonable one.
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