how do i tell an HPLC-UV COA from an LC-MS one at a glance
Slightly embarrassed to be asking this, but: how do i tell an HPLC-UV COA from an LC-MS one at a glance.
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.
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.
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".
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
Removed — cropped document. Post the whole page or do not post it; the fields people crop are the fields that matter.
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.
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.
Small fix — 214nm, not 280nm. It matters here because the impurity you are asking about barely absorbs at the longer wavelength.
chromatogram or it did not happen
chromatogram or it did not happen
Adding the bit that always gets missed: the lot on the vial has to match the lot on the page, or none of this applies to your material.
axis labels included, always
Not quite. Two labs with different gradients can resolve a close-eluting impurity differently and both be reporting honestly.
- 1UV at 214nm sees the peptide bond and picks up almost everything; at 280nm…7 comments in this branch · started by u/santiago_szabo