reading related substances threads from 2024 and half of it aged badly
The title is the argument: reading related substances threads from 2024 and half of it aged badly. Here is the rest of 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. Water content 3.8%, acetate 6.2%, purity…
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.
Small fix — 214nm, not 280nm. It matters here because the impurity you are asking about barely absorbs at the longer wavelength.
Did you get the chromatogram or only the summary line?
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.
Are the related substances itemised or is it a single total?
Correction: that is net peptide content, not purity. Different number, different meaning, and the document says so if you read the row label.
That is not what the method line says. It names the technique; it does not certify the operator.
That is the catalogue certificate rather than the batch-specific one. Same layout, completely different status.
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.