[Discussion] the related substances advice in here is 2 years out of date
the related substances advice in here is 2 years out of date — a position I have arrived at slowly and would like tested.
To save the first four comments: 2 years.
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 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.
Not medical advice, obviously, and nothing here is approved for human use. One person with a spreadsheet.
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.
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.
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.
Disagree that a lower number is automatically worse. A conservative claim that survives testing is worth more than an optimistic one that does not.
a total of 0.4% tells you less than four named impurities adding to 0.6%
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".
ask for the storage condition the stability statement was written against
a certificate with no method line is decorative
Reminder: a question about a document is not an accusation about a supplier, and posts that blur the two get retitled.
Are the related substances itemised or is it a single total?
What does the method line actually say? Not the technique — the column and the gradient.
Does the lot on the vial match the lot on the page?
Correction: that is net peptide content, not purity. Different number, different meaning, and the document says so if you read the row label.
axis labels included, always
Small fix — 214nm, not 280nm. It matters here because the impurity you are asking about barely absorbs at the longer wavelength.
That is the catalogue certificate rather than the batch-specific one. Same layout, completely different status.
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.
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.
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.
I would not read a rounded figure as evasive. Plenty of documents round to one decimal as house style.
Yes. The structure of the document matters at least as much as the number printed on it.
Careful — "the metadata looks odd" is a reason to ask a question, not a conclusion. Re-issues are ordinary.
- 1Does the lot on the vial match the lot on the page?8 comments in this branch · started by u/purity_pedant
- 2The PDF creation date being later than the analysis date is usually a…7 comments in this branch · started by u/amira_dumitru