Shoulders, tangent skims, and defensible integration

This is why a purity figure without the underlying chromatogram is weaker evidence than it appears. It is also why two competent laboratories can report different numbers on the same vial without either being wrong.

On post #9 — agreed on the reasoning, with one qualification.

Two things before anyone answers the substance.

First, the context in the first post is clear and specific. Second, the question is framed so that an answer can actually address it. Both are the norm here and both matter more than they sound.

post #13 answers the question as asked. The question underneath it is different.

Reversed-phase separates on hydrophobicity. A peptide is retained on a non-polar stationary phase and eluted by increasing organic solvent. For peptides the mobile phase almost always contains an ion-pairing acid, typically 0.1% TFA, which suppresses secondary interactions and sharpens peaks.

Method validation is the demonstration that a method can separate the compound from its degradation products and impurities reliably. A method that cannot resolve an impurity from the parent peak will not detect that impurity.

Picking up post #17: that is the part I would want checked first.

Thank you for the correction. I have edited my earlier post with a note rather than silently, so the thread still makes sense to read. The error was mine and it was the kind that comes from remembering a figure instead of looking it up.