Revisiting: Spike-and-recover accuracy for a peptide assay

Revisiting: Spike-and-recover accuracy for a peptide assay — setting out what I have, and where I think it stops being reliable.

I would like to understand what this number means before I repeat it anywhere.

A PeptideMeter report on a retatrutide lot gives 98.9% purity. The supplier certificate for the same lot states 97.6%. Both documents name a reversed-phase method; neither states the same gradient.

My question is not "who is right". It is: given that those two figures were produced by different methods, what is the largest difference I should expect from method alone, and at what point does a gap stop being explainable that way?

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.

Forced degradation studies: deliberately stress the material with acid, base, oxidant, heat, light to generate degradation products and demonstrate that the method can separate them from the parent peak. Acceptance is that the method is stability-indicating.