[Discussion] purity is doing more work than we give it credit for
The title is the argument: purity is doing more work than we give it credit for. Here is the rest of it.
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.
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.
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.
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
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.
That is the catalogue certificate rather than the batch-specific one. Same layout, completely different status.
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?
Batch number and date of analysis, are both on there?
Yes. The structure of the document matters at least as much as the number printed on it.
Area percent or net peptide content? They answer different questions.
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.
Agreed — the itemised related substances table is the difference between a document and a receipt.
Are the related substances itemised or is it a single total?
How to ask for a batch record without it turning into a negotiation.
One email, three requests: the batch-specific certificate for lot X, the method line behind it, and the storage condition the stability statement was written against. No preamble, no explanation of why you want it.
What comes back is the signal. A full document with the column and gradient printed on it, inside a day, tells you there is a real quality system behind the operation. That is the test I run before I order from anyone new, and it costs nothing.
Right, and net peptide content is where the counterion and the water go. Both numbers can be honest and very different.
net peptide content and purity are two different numbers on the same vial
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.
Related substances itemised individually is a much stronger document than a single total, because it tells you the shape of the impurity profile rathe
Disagree on this specific point. Two honest labs can resolve that impurity differently and report different numbers.
Reminder: a question about a document is not an accusation about a supplier, and posts that blur the two get retitled.
Small fix — 214nm, not 280nm. It matters here because the impurity you are asking about barely absorbs at the longer wavelength.
ask for the storage condition the stability statement was written against
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.
Net peptide content is the fraction of the powder that is actually peptide once counterion, water and residual solvent are accounted for.
This is the sentence to take away. The rest of the thread is footnotes to it.
Is water content on the document? It changes your concentration arithmetic.
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.
The document I was worried about turned out to be a re-issue with a later creation date. Asked, got the original, entirely ordinary.