Coming back to: Resolution and tailing factor: real acceptance criteria

System suitability testing: injections run before and during the sample run to establish whether the instrument, column and method were performing when the sample was analysed. If suitability did not pass, the sample results from that run are uninterpretable.

This follows post #35 rather than contradicting it.

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.

Worth separating two things that post #60 runs together.

Before anything else: what was the gradient, and at what wavelength? Area percent at different wavelengths is not the same number even on the same sample because different species absorb differently at different wavelengths. With the method stated, I can tell you something useful. Without it, all I can say is that there is one large peak.

Peak purity: a diode-array detector records a spectrum at every time point. If a peak contains two co-eluting species with different spectra, the spectrum changes across the peak. A passing peak-purity result says the spectrum is constant; it is weak evidence of homogeneity if the impurities have similar spectra.

I disagree with the reply above, and I think the disagreement is substantive rather than terminological.

The distinction being drawn does not survive when you look at the published data for this specific question. I would be glad to be shown wrong on this, because the version I am arguing against is more convenient.

For anyone arriving from a search: the marked solution above is the direct answer, and the replies underneath it add the caveats that make it safe to use.

This follows post #93 rather than contradicting it.

Before anything else: what was the gradient, and at what wavelength? Area percent at different wavelengths is not the same number even on the same sample because different species absorb differently at different wavelengths. With the method stated, I can tell you something useful. Without it, all I can say is that there is one large peak.

post #101 answers the question as asked. The question underneath it is different.

For anyone arriving from a search: the marked solution above is the direct answer, and the replies underneath it add the caveats that make it safe to use.

On post #105 — agreed on the reasoning, with one qualification.

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.