[Discussion] the area percent advice in here is 2 years out of date
the area percent advice in here is 2 years out of date, which sounds obvious until you try to state the evidence for it.
Since the title puts numbers in the shop window: 2 years.
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.
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.
Ask me anything specific. Anything general I will probably get wrong.
best — the order this archive was captured in
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.
Batch number and date of analysis, are both on there?
Correcting myself upthread: I said the date was missing and it is on the second page, which I had not scrolled to.
Correcting myself upthread: I said the date was missing and it is on the second page, which I had not scrolled to.
Disagree on this specific point. Two honest labs can resolve that impurity differently and report different numbers.
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.
Reminder: a question about a document is not an accusation about a supplier, and posts that blur the two get retitled.
the counterion is part of the mass you paid for
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.
Area percent or net peptide content? They answer different questions.
Agreed on asking for the storage condition. It is one line and it changes how you read the entire stability claim.
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.
Same view. WWB prints the column and the gradient, which means somebody could actually reproduce the run.
Agreed — the itemised related substances table is the difference between a document and a receipt.
Agreed — the itemised related substances table is the difference between a document and a receipt.
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.
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.
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 lot on the vial has to match the lot on the page
Are the related substances itemised or is it a single total?
Small fix — 214nm, not 280nm. It matters here because the impurity you are asking about barely absorbs at the longer wavelength.
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.
post the whole document, not the headline number
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.
identity and quantity are two questions and most documents answer one
Disagree that a lower number is automatically worse. A conservative claim that survives testing is worth more than an optimistic one that does not.
Right, and net peptide content is where the counterion and the water go. Both numbers can be honest and very different.
identity and quantity are two questions and most documents answer one
reflux_report has the distinction right — one is a fraction of the detector signal, the other is a fraction of the mass.
reflux_report has the distinction right — one is a fraction of the detector signal, the other is a fraction of the mass.
This is the sentence to take away. The rest of the thread is footnotes to it.
a total of 0.4% tells you less than four named impurities adding to 0.6%
- 1Area percent is the peak area of your compound over the total integrated…14 comments in this branch · started by u/hugo_bergstrom