Accepted answer
It tells you 98.4 per cent of the integrated area came off a C18 column where survodutide comes off, and the remaining 1.6 per cent did not. That is an area statement at one wavelength, not a mass statement about the vial: 1.6 per cent of area is only 1.6 per cent of mass if every impurity absorbs exactly as strongly as the parent, which none of them do. It also says nothing about how many milligrams are in the glass — water, counter-ion and a short fill are all invisible to it. What a C18 column does add is a constraint on what could be hiding: a column that retains by hydrophobicity separates deletion sequences well and separates isomers of identical hydrophobicity not at all.
The part that matters: the chemistry of peptides at low pH and high organic-solvent concentration is not something most users have intuition for, which is why published methods exist.
Proline-rich sequences are particularly problematic because the isomerisation kinetics are in the same timescale as the separation, leading to split or broadened peaks at low temperature.
Mobile phase pH at the point where you inject must match the mobile phase pH at the start of the gradient, or the sample will not be focused at the column head.
The resolving power of a separation is quantified by the resolution parameter R, defined from the heights and widths of adjacent peaks, and pharmacopoeial methods typically demand R greater than 1.5 for a method to be considered validated.
If two labs give different numbers, the method difference is the first hypothesis, not lab quality.
4Which wavelength was the purity integrated at? It changes the number more than people think. – kirsi_lahtinen 2 months ago 3Confirming from the other direction: I ignored the method section once and paid for it. – tri_gly_ala 6 days ago add a comment