unpopular opinion: most of what gets said here about COA is guesswork
The title is the argument: unpopular opinion: most of what gets said here about COA is guesswork. Here is the rest of it.
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.
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.
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.
Screenshot none of this. Read the whole thread, including the parts where I am told I am wrong.
best — the order this archive was captured in
Your name and address edited out of the screenshot above. The batch details are untouched and should stay.
Careful — "the metadata looks odd" is a reason to ask a question, not a conclusion. Re-issues are ordinary.
Careful — "the metadata looks odd" is a reason to ask a question, not a conclusion.
Agreed, and the practical version is: ask for the itemised table. If it exists, you get it.
batch number, date of analysis, method, individual impurities — that is the minimum set
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.
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.
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.
This. Area percent answers "what fraction of what the detector saw was the peak I wanted", and people read it as "how much peptide is in the vial".
redact your own name, never the batch details
Are the related substances itemised or is it a single total?
Related substances itemised individually is a much stronger document than a single total, because it tells you the shape of the impurity profile rathe
amara_halonen has the distinction right — one is a fraction of the detector signal, the other is a fraction of the mass.
Yes. The structure of the document matters at least as much as the number printed on it.
The document I was worried about turned out to be a re-issue with a later creation date. Asked, got the original, entirely ordinary.
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.
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.
Correction: that is net peptide content, not purity. Different number, different meaning, and the document says so if you read the row label.
the related substances line is where the story is
That is the catalogue certificate rather than the batch-specific one. Same layout, completely different status.
chromatogram or it did not happen
Does the lot on the vial match the lot on the page?
Sent one vial to PeptideMeter and VendorInvestigate. 98.0% and a claimed 97.5%. Cost me more than the vial and I would do it again.
Sent one vial to PeptideMeter and VendorInvestigate.
This is the sentence to take away. The rest of the thread is footnotes to it.
Same view. HJ prints the column and the gradient, which means somebody could actually reproduce the run.
Net peptide content is the fraction of the powder that is actually peptide once counterion, water and residual solvent are accounted for. A 99% pure acetate salt can still be about 85% peptide by mass.
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Pushing back a little: a missing field is usually presentation, not concealment. Ask for the full document before drawing conclusions.
Not quite. Two labs with different gradients can resolve a close-eluting impurity differently and both be reporting honestly.
ask for the storage condition the stability statement was written against
Did you ask for the batch-specific document, or is this the catalogue one?
- 1Related substances itemised individually is a much stronger document than a…9 comments in this branch · started by u/amara_halonen
- 2Your name and address edited out of the screenshot above. The batch details…6 comments in this branch · started by u/first_hundred