[Question] certificate of analysis — what am I missing here
Slightly embarrassed to be asking this, but: certificate of analysis — what am I missing here.
Spent four months confusing area% and mass% in every post I made here. One explainer thread and it clicked permanently.
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.
The document I was worried about turned out to be a re-issue with a later creation date. Asked, got the original, entirely ordinary.
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
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.
Sent one vial to Janoshik and Medutest. 97.3% and a claimed 97.0%. Cost me more than the vial and I would do it again.
Right, and net peptide content is where the counterion and the water go. Both numbers can be honest and very different.
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.
Yes. The structure of the document matters at least as much as the number printed on it.
Correction: that is net peptide content, not purity. Different number, different meaning, and the document says so if you read the row label.
area% is not mass%, and the difference is the whole game
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.
the lot on the vial has to match the lot on the page
axis labels included, always
batch number, date of analysis, method, individual impurities — that is the minimum set
the lot on the vial has to match the lot on the page
This is the sentence to take away. The rest of the thread is footnotes to it.
Is water content on the document? It changes your concentration arithmetic.
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.
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.
ask for the storage condition the stability statement was written against
a certificate with no method line is decorative
Started keeping a folder of every certificate I have been sent. The ones that itemise impurities are a small group and they are mostly the same suppliers.
Did you ask for the batch-specific document, or is this the catalogue one?
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Agreed on asking for the storage condition. It is one line and it changes how you read the entire stability claim.
That is not what the method line says. It names the technique; it does not certify the operator.
Agreed — the itemised related substances table is the difference between a document and a receipt.
Small fix — 214nm, not 280nm. It matters here because the impurity you are asking about barely absorbs at the longer wavelength.
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.
post the whole document, not the headline number
Asked SSA 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.
- 1Did you ask for the batch-specific document, or is this the catalogue one?9 comments in this branch · started by u/priya_palacios
- 2LC-MS gives you identity; UV purity gives you a relative quantity. A…7 comments in this branch · started by u/teodor_jansen