three years of related substances threads, summarised so you do not have to read them
three years of related substances threads, summarised so you do not have to read them, and I am aware this is a minority view on this board.
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.
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.
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.
Please do not ask me what dose you should be on. I genuinely do not know and neither does anyone else here.
best — the order this archive was captured in
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.
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.
Agreed on asking for the storage condition. It is one line and it changes how you read the entire stability claim.
Right, and net peptide content is where the counterion and the water go. Both numbers can be honest and very different.
the related substances line is where the story is
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.
My first certificate had a compound name, a percentage and a logo.
noor_cardoso has the distinction right — one is a fraction of the detector signal, the other is a fraction of the mass.
Reminder: a question about a document is not an accusation about a supplier, and posts that blur the two get retitled.
water content is on there and everyone skips it
the lot on the vial has to match the lot on the page
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
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.
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.
The PDF creation date being later than the analysis date is usually a re-issue or a re-export.
This is the sentence to take away. The rest of the thread is footnotes to it.
Careful — "the metadata looks odd" is a reason to ask a question, not a conclusion. Re-issues are ordinary.
area% is not mass%, and the difference is the whole game
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.
a certificate with no method line is decorative
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.
post the whole document, not the headline number
a total of 0.4% tells you less than four named impurities adding to 0.6%
a total of 0.4% tells you less than four named impurities adding to 0.6%
Disagree on this specific point. Two honest labs can resolve that impurity differently and report different numbers.
batch number, date of analysis, method, individual impurities — that is the minimum set
identity and quantity are two questions and most documents answer one
- 1Right, and net peptide content is where the counterion and the water go.…8 comments in this branch · started by u/liv_nkemelu
- 2a certificate with no method line is decorative7 comments in this branch · started by u/bastian_moreau