water content is on the COA and everyone skips it
water content is on the COA and everyone skips it — a position I have arrived at slowly and would like tested.
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".
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.
Ask me anything specific. Anything general I will probably get wrong.
best — the order this archive was captured in
Removed — cropped document. Post the whole page or do not post it; the fields people crop are the fields that matter.
Removed — cropped document.
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.
That is the catalogue certificate rather than the batch-specific one. Same layout, completely different status.
Small fix — 214nm, not 280nm. It matters here because the impurity you are asking about barely absorbs at the longer wavelength.
[removed by moderator]
Correction: that is net peptide content, not purity. Different number, different meaning, and the document says so if you read the row label.
Agreed — the itemised related substances table is the difference between a document and a receipt.
- 1Related substances itemised individually is a much stronger document than a…6 comments in this branch · started by u/liv_nkemelu