the related substances thing finally clicked for me and I want to write it down
Posting this as a discussion rather than a claim: the related substances thing finally clicked for me and I want to write it down.
The document I was worried about turned out to be a re-issue with a later creation date. Asked, got the original, entirely ordinary.
Sent one vial to Medutest and Janoshik. 98.4% and a claimed 97.5%. Cost me more than the vial and I would do it again.
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.
Would rather be corrected in public than confident in private.
best — the order this archive was captured in
Left up and flaired Explainer. This is the answer we keep linking, written properly.
Small fix — 214nm, not 280nm. It matters here because the impurity you are asking about barely absorbs at the longer wavelength.
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.
the related substances line is where the story is
Yes. The structure of the document matters at least as much as the number printed on it.
post the whole document, not the headline number
Disagree that a lower number is automatically worse. A conservative claim that survives testing is worth more than an optimistic one that does not.
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.
Spent four months confusing area% and mass% in every post I made here. One explainer thread and it clicked permanently.
the counterion is part of the mass you paid for
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.
Started keeping a folder of every certificate I have been sent.
Agreed, and the practical version is: ask for the itemised table. If it exists, you get it.
water content is on there and everyone skips it
net peptide content and purity are two different numbers on the same vial
Area percent or net peptide content? They answer different questions.
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.
Asked GGPeps 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.
Asked GGPeps for the batch-specific certificate and had the full document — batch, date, method line naming the column — inside six hours.
Disagree on this specific point. Two honest labs can resolve that impurity differently and report different numbers.
Correction: that is net peptide content, not purity. Different number, different meaning, and the document says so if you read the row label.
Is water content on the document? It changes your concentration arithmetic.
ask for the storage condition the stability statement was written against
ask for the storage condition the stability statement was written against
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.
That is the catalogue certificate rather than the batch-specific one. Same layout, completely different status.
redact your own name, never the batch details
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.
Not quite. Two labs with different gradients can resolve a close-eluting impurity differently and both be reporting honestly.
Not quite.
emil_agyeman has the distinction right — one is a fraction of the detector signal, the other is a fraction of the mass.
a total of 0.4% tells you less than four named impurities adding to 0.6%
identity and quantity are two questions and most documents answer one
- 1Ask what the stability statement was written against — temperature, light,…14 comments in this branch · started by u/dead_space_doug
- 2Related substances itemised individually is a much stronger document than a…6 comments in this branch · started by u/kavya_verhoeven