certificate of analysis — 18 things I got wrong before I got it right
The title is the argument: certificate of analysis — 18 things I got wrong before I got it right. Here is the rest of it.
Area percent is the peak area of your compound over the total integrated area, at one wavelength, on one gradient. It is a relative measure of what the detector saw, not a mass fraction of the vial.
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".
If somebody has the same thing measured a different way, post it next to mine and we will see whether they agree.
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.
Did you ask for the batch-specific document, or is this the catalogue one?
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.
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.
Agreed — the itemised related substances table is the difference between a document and a receipt.
Left up and flaired Explainer. This is the answer we keep linking, written properly.
Correction: that is net peptide content, not purity. Different number, different meaning, and the document says so if you read the row label.
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.
chromatogram or it did not happen
That is the catalogue certificate rather than the batch-specific one. Same layout, completely different status.
Not quite. Two labs with different gradients can resolve a close-eluting impurity differently and both be reporting honestly.
I would not read a rounded figure as evasive. Plenty of documents round to one decimal as house style.
Does the lot on the vial match the lot on the page?
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.