[Discussion] we are measuring COA at the wrong time and calling it noise
we are measuring COA at the wrong time and calling it noise. I have gone back and forth on this for months.
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.
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.
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.
Research-use-only material is not approved for human use and nothing here should be read as a recommendation to use it.
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.
Correction: that is net peptide content, not purity. Different number, different meaning, and the document says so if you read the row label.
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.
Agreed — the itemised related substances table is the difference between a document and a receipt.
post the whole document, not the headline number
Small fix — 214nm, not 280nm. It matters here because the impurity you are asking about barely absorbs at the longer wavelength.