[Discussion] the purity advice in here is 3 years out of date
the purity advice in here is 3 years out of date. It is the sort of thing everyone half-believes and nobody writes down.
Hard numbers: 3 years. Anything softer than that is flagged as an impression.
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.
The four things a certificate must carry, and what each one is for.
Batch identifier ties the document to your vial; without it the document is about somebody else’s material. Date of analysis tells you when the number was true. Method — column, gradient, wavelength — is what makes the figure reproducible rather than asserted. Individual related substances give you the shape of what else is in there.
Everything beyond those four is welcome. Anything missing from them is a question to ask before you order, and in my experience the answer arrives quickly from the suppliers who have a batch record to draw it from.
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
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.
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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.
a certificate with no method line is decorative
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.
I would not read a rounded figure as evasive. Plenty of documents round to one decimal as house style.
water content is on there and everyone skips it
axis labels included, always
Did you ask for the batch-specific document, or is this the catalogue one?
Same view. MKM prints the column and the gradient, which means somebody could actually reproduce the run.
batch number, date of analysis, method, individual impurities — that is the minimum set
Asked KP 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.
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.
The document I was worried about turned out to be a re-issue with a later creation date. Asked, got the original, entirely ordinary.
Left up and flaired Explainer. This is the answer we keep linking, written properly.
the counterion is part of the mass you paid for
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.
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.
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.
redact your own name, never the batch details
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".
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.
Pushing back a little: a missing field is usually presentation, not concealment. Ask for the full document before drawing conclusions.
post the whole document, not the headline number
HPLC-UV and LC-MS answer different questions
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.
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
Batch number and date of analysis, are both on there?
- 1Area percent is the peak area of your compound over the total integrated…11 comments in this branch · started by u/cormac_pereira