Posting this under the heading it deserves: Deamidation and the close-eluting pair it produces — the long version Everything below is what sits behind that.
A narrow question about Deamidation, 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.
The opening post and I disagree about the size of the effect, not about the direction.
Racemisation produces a diastereomer that is mass-identical and chromatographically resolvable only on a method chosen for the purpose. Standard reversed-phase frequently will not separate 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.
On reflection I would soften that slightly.
Reading back through the Deamidation threads from last year, the same three questions come up every time and only one of them has ever been answered properly. That seems like a documentation gap rather than a knowledge gap.
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