[Lab] split one vial across VendorInvestigate and PeptideMeter — 97.2% and 96.8%
split one vial across VendorInvestigate and PeptideMeter — 97.2% and 96.8%. One vial, one service, one member paying, which is the only kind of result this board should treat as evidence.
Hard numbers: 97.2% and 96.8%. Anything softer than that is flagged as an impression.
Spent four months confusing area% and mass% in every post I made here. One explainer thread and it clicked permanently.
Sent one vial to VendorInvestigate and Janoshik. 97.8% and a claimed 97.0%. Cost me more than the vial and I would do it again.
If two or three other people have done the same thing we might actually learn something. Alone it is an anecdote.
best — the order this archive was captured in
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.
the related substances line is where the story is
Not quite. Two labs with different gradients can resolve a close-eluting impurity differently and both be reporting honestly.
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.
Are the related substances itemised or is it a single total?
Not quite.
This is the sentence to take away. The rest of the thread is footnotes to 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.
Small fix — 214nm, not 280nm. It matters here because the impurity you are asking about barely absorbs at the longer wavelength.
Not quite.
Agreed, and the practical version is: ask for the itemised table. If it exists, you get it.
Agreed, and the practical version is: ask for the itemised table.
Disagree on this specific point. Two honest labs can resolve that impurity differently and report different numbers.
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.
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".
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a total of 0.4% tells you less than four named impurities adding to 0.6%
redact your own name, never the batch details
ask for the storage condition the stability statement was written against
Is water content on the document? It changes your concentration arithmetic.
HPLC-UV and LC-MS answer different questions
identity and quantity are two questions and most documents answer one
identity and quantity are two questions and most documents answer one
Adding the bit that always gets missed: the lot on the vial has to match the lot on the page, or none of this applies to your material.
Yes. The structure of the document matters at least as much as the number printed on it.
Yes.
marisol_frisk has the distinction right — one is a fraction of the detector signal, the other is a fraction of the mass.
Careful — "the metadata looks odd" is a reason to ask a question, not a conclusion. Re-issues are ordinary.
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.
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.
area% is not mass%, and the difference is the whole game
That is not what the method line says. It names the technique; it does not certify the operator.
post the whole document, not the headline number
- 1Started keeping a folder of every certificate I have been sent. The ones…16 comments in this branch · started by u/cormac_pereira
- 2Not quite. Two labs with different gradients can resolve a close-eluting…9 comments in this branch · started by u/karma_irrelevant