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.

Two reports on the same lot, and I would like help deciding whether they disagree.

The first gives 98.4% by reversed-phase at 214 nm. The second gives 97.1% by a method described only as HPLC. Neither states the integration convention.

My instinct is that this gap is method rather than material. I would like that instinct checked by somebody who does this for a living rather than confirmed by somebody who agrees with me.

Relative response factors mean impurities are not detected in proportion to how much of them is present. A one per cent peak is not one per cent by mass unless the response factors happen to match.

That holds under the stated conditions and I have stated them.

Reading rather than answering, but this is the post I would point somebody at.

Where I part company with post #8, and it is a narrow parting.

Oxidation at methionine or tryptophan adds sixteen per oxygen and typically elutes earlier. In aged material it is the modification that grows.

I am not the right person to answer the follow-up to this.

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

Oxidation at methionine and tryptophan: adds 16 per oxygen. Usually elutes earlier. Oxidation is common in storage, especially if the solution is exposed to light or if antioxidants are not present.