[Discussion] related substances are doing more work than we give it credit for
related substances are doing more work than we give it credit for, and I am aware this is a minority view on this board.
Sent one vial to VendorInvestigate and Janoshik. 98.9% and a claimed 98.0%. Cost me more than the vial and I would do it again.
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.
Asked HJ 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.
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
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.
Correction: that is net peptide content, not purity. Different number, different meaning, and the document says so if you read the row label.
Does the lot on the vial match the lot on the page?
Yes. The structure of the document matters at least as much as the number printed on it.
Yes.
Agreed, and the practical version is: ask for the itemised table. If it exists, you get it.
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.
ask for the storage condition the stability statement was written against
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.
Water content 3.8%, acetate 6.2%, purity 99%, net peptide about 90% of label weight.
valeria_karlsen has the distinction right — one is a fraction of the detector signal, the other is a fraction of the mass.
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.
Are the related substances itemised or is it a single total?
Disagree that a lower number is automatically worse. A conservative claim that survives testing is worth more than an optimistic one that does not.
area% is not mass%, and the difference is the whole game
water content is on there and everyone skips it
batch number, date of analysis, method, individual impurities — that is the minimum set
Small fix — 214nm, not 280nm. It matters here because the impurity you are asking about barely absorbs at the longer wavelength.
batch number, date of analysis, method, individual impurities — that is the minimum set
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.
Did you get the chromatogram or only the summary line?
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.
HPLC-UV and LC-MS answer different questions
Not quite. Two labs with different gradients can resolve a close-eluting impurity differently and both be reporting honestly.
That is not what the method line says. It names the technique; it does not certify the operator.
axis labels included, always
Did you ask for the batch-specific document, or is this the catalogue one?
Correcting myself upthread: I said the date was missing and it is on the second page, which I had not scrolled to.
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.
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".
a certificate with no method line is decorative
the related substances line is where the story is
net peptide content and purity are two different numbers on the same vial
- 1Water content 3.8%, acetate 6.2%, purity 99%, net peptide about 90% of label…11 comments in this branch · started by u/valeria_karlsen
- 2UV at 214nm sees the peptide bond and picks up almost everything; at 280nm…7 comments in this branch · started by u/stablecoin_steve