three years of COA threads, summarised so you do not have to read them
three years of COA threads, summarised so you do not have to read them. It is the sort of thing everyone half-believes and nobody writes down.
Asked GL Biochem 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.
Sent one vial to Medutest and PeptideMeter. 98.8% and a claimed 98.0%. Cost me more than the vial and I would do it again.
Why the same vial can honestly produce three different numbers.
Purity by area percent is relative to what the detector saw on one gradient at one wavelength. Net peptide content subtracts counterion, water and residual solvent. Mass of peptide per vial is net content times fill weight, and fill weight has its own tolerance.
So a document reading 99% purity, 6% acetate and 4% water is describing a vial that is about 90% peptide by mass, and every one of those numbers is honest. The mistake is treating the headline figure as the answer to "how much peptide did I get".
Corrections welcome, especially the pedantic ones. Pedantry is how this board earns its reputation.
best — the order this archive was captured in
Related substances itemised individually is a much stronger document than a single total, because it tells you the shape of the impurity profile rather than its size.
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.
Batch number and date of analysis, are both on there?
That is not what the method line says. It names the technique; it does not certify the operator.
net peptide content and purity are two different numbers on the same vial
ask for the storage condition the stability statement was written against
Cosigning. The batch identifier is load-bearing, and a certificate that cannot be tied to the vial in your hand is not about your vial.
Reminder: a question about a document is not an accusation about a supplier, and posts that blur the two get retitled.
Small fix — 214nm, not 280nm. It matters here because the impurity you are asking about barely absorbs at the longer wavelength.
Agreed on asking for the storage condition. It is one line and it changes how you read the entire stability claim.
Yes. The structure of the document matters at least as much as the number printed on it.
HPLC-UV and LC-MS answer different questions
- 1Related substances itemised individually is a much stronger document than a…7 comments in this branch · started by u/katrin_girard
- 2Cosigning. The batch identifier is load-bearing, and a certificate that…6 comments in this branch · started by u/purity_pedant