Endotoxin and why it is a separate question from purity — what changed since

On Endotoxin, I would rather understate and be corrected upward than overstate and be quoted. That is a house style here and it is a good one.

This is the first time the answer has come with its own limits attached. Appreciated.

Endotoxin is well covered in the tag pages, and the older discussions are better than the recent ones because they were argued out properly. Worth twenty minutes before adding to this one.

Sensible. I would want the same detail before I acted on it either.

Where I part company with post #66, and it is a narrow parting.

Off-target structures: if the sequence synthesis goes wrong, a completely different amino acid can be incorporated. The resulting off-target peptide is a structural isomer with the same mass but a different sequence. No chromatographic purity method detects this without a reference standard.

The arithmetic in post #69 is right; the assumption feeding it is the part to check.

I would be cautious about generalising from the Endotoxin example above. It is a good example. It is one example.

Comparing impurity profiles across suppliers is much more informative than comparing purity figures, and almost nobody has the documents to do it.

That is the practical version. The rigorous version is longer and says the same thing.

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.

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