Coming back to: What consumer-accessible tests can and cannot determine

Asking directly, because I could not find a straight answer: What consumer-accessible tests can and cannot determine

Something about consumer-accessible tests does not reconcile and I would like a second pair of eyes before I decide which half is wrong.

Two sources, both reputable, giving figures that cannot both be right unless they are measuring different quantities. My suspicion is that they are, and I cannot see how.

Enzyme assays: if you have an enzyme that reacts specifically with your compound, an enzyme-based assay can work. These are sometimes available commercially but are less common than antibody-based tests.

It cost nothing to check and would have cost something not to.

I had written a reply contradicting the opening post and deleted it. Here is what survived.

A test that gives a yes or no on the presence of peptide bonds is answering a genuinely useful question if that is the question you had. It is not a purity assay and cannot be read as one.

Adding a data point of agreement rather than a data point.

Where I part company with post #4, and it is a narrow parting.

Colorimetric tests: colour intensity correlates with concentration, but the relationship is non-linear at extremes and the correlation depends on the exact conditions (pH, temperature, timing). Reading the colour visually introduces subjectivity.

I would hold that lightly until someone with a larger sample weighs in.