[PSA] certificate of analysis is not what most of this community thinks it is
certificate of analysis is not what most of this community thinks it is. Two minutes of reading now saves an argument later.
My first certificate had a compound name, a percentage and a logo. I thought that was normal. It is not, and now I know what to ask for.
How to ask for a batch record without it turning into a negotiation.
One email, three requests: the batch-specific certificate for lot X, the method line behind it, and the storage condition the stability statement was written against. No preamble, no explanation of why you want it.
What comes back is the signal. A full document with the column and gradient printed on it, inside a day, tells you there is a real quality system behind the operation. That is the test I run before I order from anyone new, and it costs nothing.
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".
Would rather be corrected in public than confident in private.
best — the order this archive was captured in
The PDF creation date being later than the analysis date is usually a re-issue or a re-export. It is worth one question and it is not evidence of anything on its own.
I would not read a rounded figure as evasive. Plenty of documents round to one decimal as house style.
Yes — and the reason to ask for the whole page is that the interesting parts are the ones people crop out to fit a screenshot.
Right, and net peptide content is where the counterion and the water go. Both numbers can be honest and very different.
Does the lot on the vial match the lot on the page?
Not quite. Two labs with different gradients can resolve a close-eluting impurity differently and both be reporting honestly.
Reminder: a question about a document is not an accusation about a supplier, and posts that blur the two get retitled.
Did you ask for the batch-specific document, or is this the catalogue one?
Batch number and date of analysis, are both on there?
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Pushing back a little: a missing field is usually presentation, not concealment. Ask for the full document before drawing conclusions.
What does the method line actually say? Not the technique — the column and the gradient.
Disagree that a lower number is automatically worse. A conservative claim that survives testing is worth more than an optimistic one that does not.
Careful — "the metadata looks odd" is a reason to ask a question, not a conclusion. Re-issues are ordinary.
- 1Reminder: a question about a document is not an accusation about a supplier,…8 comments in this branch · started by u/coa_janitor
- 2The PDF creation date being later than the analysis date is usually a…6 comments in this branch · started by u/camila_lindqvist