purity — 3 things I got wrong before I got it right
purity — 3 things I got wrong before I got it right. Not a hot take, just something I have not seen said plainly here. 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…
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.
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.
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.
identity and quantity are two questions and most documents answer one
Does the lot on the vial match the lot on the page?
batch number, date of analysis, method, individual impurities — that is the minimum set
post the whole document, not the headline number