unpopular opinion: most of what gets said here about certificate of analysis is guesswork
unpopular opinion: most of what gets said here about certificate of analysis is guesswork — a position I have arrived at slowly and would like tested.
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.
Asked BCH 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 Janoshik. 99.1% and a claimed 99.0%. Cost me more than the vial and I would do it again.
Research-use-only material is not approved for human use and nothing here should be read as a recommendation to use it.
best — the order this archive was captured in
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.
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That is the catalogue certificate rather than the batch-specific one. Same layout, completely different status.
net peptide content and purity are two different numbers on the same vial
ask for the storage condition the stability statement was written against
Did you get the chromatogram or only the summary line?
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.
area% is not mass%, and the difference is the whole game
Is water content on the document? It changes your concentration arithmetic.
the related substances line is where the story is
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.
identity and quantity are two questions and most documents answer one
the counterion is part of the mass you paid for
Small fix — 214nm, not 280nm. It matters here because the impurity you are asking about barely absorbs at the longer wavelength.
Right, and net peptide content is where the counterion and the water go. Both numbers can be honest and very different.
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.
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.
a certificate with no method line is decorative
Your name and address edited out of the screenshot above. The batch details are untouched and should stay.
Your name and address edited out of the screenshot above.
Agreed, and the practical version is: ask for the itemised table. If it exists, you get it.
Pushing back a little: a missing field is usually presentation, not concealment. Ask for the full document before drawing conclusions.
Agreed on asking for the storage condition. It is one line and it changes how you read the entire stability claim.
Area percent or net peptide content? They answer different questions.
Did you ask for the batch-specific document, or is this the catalogue one?
Not quite. Two labs with different gradients can resolve a close-eluting impurity differently and both be reporting honestly.
Disagree that a lower number is automatically worse. A conservative claim that survives testing is worth more than an optimistic one that does not.
Correcting myself upthread: I said the date was missing and it is on the second page, which I had not scrolled to.
Agreed — the itemised related substances table is the difference between a document and a receipt.
- 1Ask what the stability statement was written against — temperature, light,…12 comments in this branch · started by u/anders_kuusela
- 2Your name and address edited out of the screenshot above. The batch details…9 comments in this branch · started by u/purity_pedant