[Meta] the area percent rule is doing its job and people should stop complaining
Housekeeping: the area percent rule is doing its job and people should stop complaining. Water content 3.8%, acetate 6.2%, purity 99%, net peptide about 90% of label weight. All four numbers honest, and I had to read it twice. Started keeping a folder of every certificate I have been sent. The ones that itemise…
identity and quantity are two questions and most documents answer one
Not quite. Two labs with different gradients can resolve a close-eluting impurity differently and both be reporting honestly.
area% is not mass%, and the difference is the whole game
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.
Small fix — 214nm, not 280nm. It matters here because the impurity you are asking about barely absorbs at the longer wavelength.
HPLC-UV and LC-MS answer different questions
net peptide content and purity are two different numbers on the same vial