Residual solvents and scavengers: what is looked for — what changed since posts 31–42

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

Reading this Residual solvents and scavengers thread as someone who came in with a fixed view: the third and seventh replies moved me and the confident ones did not.

Post #30 is the version of this I will quote in future. One addition.

On Residual solvents and scavengers, 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.

The related-substances total is only as informative as the method that generated it. Two per cent by a method that resolves everything is a different statement from two per cent by a method that resolves little.

Agreed on all of that, and I have nothing to add to it.

Scavengers and cleavage-cocktail residues can persist and appear as small early-eluting peaks. They are process-related rather than sequence-related, which is a useful distinction when reading a profile.

Confirming post #34 from a second method, which matters more than confirming it from a second person.

Filing a mild objection to the consensus on Residual solvents and scavengers. Mild because I might be wrong; an objection because nobody has addressed the case that does not fit.

I had written a reply contradicting post #36 and deleted it. Here is what survived.

Residual solvents and scavengers was covered in the wiki last year and the page has a review date on it, which is a better starting point than my memory of a thread.

Narrowing post #38, because the general version has more than one answer.

Dimer and higher-order multimers: two or more peptide molecules bonded together. They appear at double the mass and higher. They may or may not separate from the monomer on HPLC depending on the method.

That is what I would do. It may not be what is correct.

What I want from this Residual solvents and scavengers thread is the list of things that would need to be true for the claim to hold. If we can write that list, we can check it.

Post #37 put the caveat in the right place and I want to underline it.

Residual solvents and scavengers has been discussed here with more heat than it deserves, mostly because two definitions have been in play the whole time.

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.