Purity claim inflation (revision 15)

Purity claim inflation is the presentation of a purity figure in a manner that overstates what it establishes. Unlike forgery, the figure is generally genuine: what is misleading is the method that produced it, the way it was integrated, or the framing that presents it as answering a question it does not answer.^[1]

The most consequential form is the substitution of purity for content. An area percent figure is normalised: it describes the proportion of detected material attributable to the main peak, and it is unaffected by how much peptide is present. A vial can be 99% pure and contain half the stated mass. Presenting purity where content is the relevant question is the commonest inflation of all.^[1]

Because these practices operate through selection rather than fabrication, they are not detectable by asking whether a report is genuine. They are detectable, if at all, by reading what the report actually measured.

None of these is necessarily improper. A short gradient may be entirely appropriate for a well-characterised material; aggregate reporting of related substances is standard in some contexts. What makes a presentation inflationary is the gap between what the method establishes and what the figure is used to assert.^[2]

The detection-wavelength point is the least appreciated. Peptide purity is usually determined at 214 nm, where the amide bond absorbs, so response is roughly proportional to the number of bonds and impurities are detected reasonably. A determination at 280 nm, where aromatic side chains absorb, will systematically under-detect impurities lacking those residues. Both are legitimate methods; they do not answer the same question.

An area percent purity figure establishes that, of the material detected by that detector under those conditions, the stated proportion eluted as the main peak. That is a real and useful fact and this article should not be read as dismissing it.^[1]

What it does not establish: how much peptide is in the vial; that the main peak is the intended molecule; that undetected species are absent; that the figure would be reproduced on a different method.

A complete characterisation therefore requires, at minimum, identity by mass, purity by a specified chromatographic method, content, and water. Certificates supplying all four are a minority in submissions to this wiki, though all four are ordinary components of a specification where one exists.^[3] A certificate supplying only the second is not thereby dishonest — but a claim about how much active substance a vial contains cannot rest on it.^[4]

• Area percent purity
• Peptide content
• Certificate of analysis
• Test report forgery
• Analytical method validation