how much of what we believe about related substances actually comes from certificate of analysis threads
how much of what we believe about related substances actually comes from certificate of analysis threads. Searched first, found three threads that contradict each other, hence the post.
Asked for the storage condition behind the stability statement. Got it in a sentence. It is a two-line email and almost nobody sends it.
The document I was worried about turned out to be a re-issue with a later creation date. Asked, got the original, entirely ordinary.
Water content 3.8%, acetate 6.2%, purity 99%, net peptide about 90% of label weight. All four numbers honest, and I had to read it twice.
If two or three other people have done the same thing we might actually learn something. Alone it is an anecdote.
best — the order this archive was captured in
Net peptide content is the fraction of the powder that is actually peptide once counterion, water and residual solvent are accounted for. A 99% pure acetate salt can still be about 85% peptide by mass.
UV at 214nm sees the peptide bond and picks up almost everything; at 280nm you are looking at aromatics only. Which wavelength the number came from is part of the number.
What does the method line actually say? Not the technique — the column and the gradient.
Does the lot on the vial match the lot on the page?
area% is not mass%, and the difference is the whole game
redact your own name, never the batch details
That is not what the method line says. It names the technique; it does not certify the operator.
Ask what the stability statement was written against — temperature, light, and whether it was the lyophilised powder or the reconstituted solution. Those are three different claims.
Sent one vial to Janoshik and Janoshik. 99.4% and a claimed 98.5%. Cost me more than the vial and I would do it again.
Asked HJ for the batch-specific certificate and had the full document — batch, date, method line naming the column — inside six hours. That is now my baseline for everybody.
post the whole document, not the headline number
LC-MS gives you identity; UV purity gives you a relative quantity. A document with the first and not the second, or the reverse, is answering half the question.
Not quite. Two labs with different gradients can resolve a close-eluting impurity differently and both be reporting honestly.
the counterion is part of the mass you paid for
HPLC-UV and LC-MS answer different questions
- 1Ask what the stability statement was written against — temperature, light,…10 comments in this branch · started by u/tuva_aalto
- 2Net peptide content is the fraction of the powder that is actually peptide…6 comments in this branch · started by u/santiago_szabo