[Question] is 99.0% actually fine or am I being sold a rounding error
The claim in the title is exactly the claim I am making: is 99.0% actually fine or am I being sold a rounding error. Nothing implied beyond it.
To save the first four comments: 99.0%.
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.
If somebody has the same thing measured a different way, post it next to mine and we will see whether they agree.
best — the order this archive was captured in
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.
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.
I would not read a rounded figure as evasive. Plenty of documents round to one decimal as house style.
the counterion is part of the mass you paid for
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".
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.
ask for the storage condition the stability statement was written against
That is not what the method line says. It names the technique; it does not certify the operator.
a total of 0.4% tells you less than four named impurities adding to 0.6%
batch number, date of analysis, method, individual impurities — that is the minimum set
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.
Area percent or net peptide content? They answer different questions.
Correction: that is net peptide content, not purity. Different number, different meaning, and the document says so if you read the row label.
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.
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.
Small fix — 214nm, not 280nm. It matters here because the impurity you are asking about barely absorbs at the longer wavelength.
area% is not mass%, and the difference is the whole game
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.
Agreed — the itemised related substances table is the difference between a document and a receipt.
a certificate with no method line is decorative
That is the catalogue certificate rather than the batch-specific one. Same layout, completely different status.
chromatogram or it did not happen
HPLC-UV and LC-MS answer different questions
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.
water content is on there and everyone skips it
Agreed on asking for the storage condition. It is one line and it changes how you read the entire stability claim.
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.
- 1Related substances itemised individually is a much stronger document than a…11 comments in this branch · started by u/sofia_ferreira
- 2Net peptide content is the fraction of the powder that is actually peptide…9 comments in this branch · started by u/clara_danquah