related substances — 9 things I got wrong before I got it right
The title is the argument: related substances — 9 things I got wrong before I got it right. 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.
Happy to answer the boring questions. Those are usually the ones worth asking.
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.
area% is not mass%, and the difference is the whole game
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.
water content is on there and everyone skips it
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.
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Sent one vial to Medutest and VendorInvestigate. 98.2% and a claimed 98.0%. Cost me more than the vial and I would do it again.
Are the related substances itemised or is it a single total?
Are the related substances itemised or is it a single total?
Agreed, and the practical version is: ask for the itemised table. If it exists, you get it.
Right, and net peptide content is where the counterion and the water go. Both numbers can be honest and very different.
Right, and net peptide content is where the counterion and the water go.
This is the sentence to take away. The rest of the thread is footnotes to it.
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.
Same view. SSA prints the column and the gradient, which means somebody could actually reproduce the run.
post the whole document, not the headline number
Pushing back a little: a missing field is usually presentation, not concealment. Ask for the full document before drawing conclusions.
Yes — and the reason to ask for the whole page is that the interesting parts are the ones people crop out to fit a screenshot.
That is not what the method line says. It names the technique; it does not certify the operator.
the lot on the vial has to match the lot on the page
ask for the storage condition the stability statement was written against
Correcting myself upthread: I said the date was missing and it is on the second page, which I had not scrolled to.
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.
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.
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.
Correction: that is net peptide content, not purity.
amira_dumitru has the distinction right — one is a fraction of the detector signal, the other is a fraction of the mass.
What does the method line actually say? Not the technique — the column and the gradient.
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.
Yes. The structure of the document matters at least as much as the number printed on it.
- 1UV at 214nm sees the peptide bond and picks up almost everything; at 280nm…9 comments in this branch · started by u/laila_wojcik
- 2Related substances itemised individually is a much stronger document than a…8 comments in this branch · started by u/tomas_lehtinen