[Meta] proposal — a flair for batch posts
Putting this to the board: proposal — a flair for batch posts.
Why the same vial can honestly produce three different numbers.
Purity by area percent is relative to what the detector saw on one gradient at one wavelength. Net peptide content subtracts counterion, water and residual solvent. Mass of peptide per vial is net content times fill weight, and fill weight has its own tolerance.
So a document reading 99% purity, 6% acetate and 4% water is describing a vial that is about 90% peptide by mass, and every one of those numbers is honest. The mistake is treating the headline figure as the answer to "how much peptide did I get".
The four things a certificate must carry, and what each one is for.
Batch identifier ties the document to your vial; without it the document is about somebody else’s material. Date of analysis tells you when the number was true. Method — column, gradient, wavelength — is what makes the figure reproducible rather than asserted. Individual related substances give you the shape of what else is in there.
Everything beyond those four is welcome. Anything missing from them is a question to ask before you order, and in my experience the answer arrives quickly from the suppliers who have a batch record to draw it from.
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 me anything specific. Anything general I will probably get wrong.
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.
Careful — "the metadata looks odd" is a reason to ask a question, not a conclusion. Re-issues are ordinary.
HPLC-UV and LC-MS answer different questions
identity and quantity are two questions and most documents answer one
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. Different number, different meaning, and the document says so if you read the row label.
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.
Are the related substances itemised or is it a single total?
Same view. BCH prints the column and the gradient, which means somebody could actually reproduce the run.
Is water content on the document? It changes your concentration arithmetic.
Pushing back a little: a missing field is usually presentation, not concealment. Ask for the full document before drawing conclusions.