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.

Confirming post #2 from a second method, which matters more than confirming it from a second person.

What you can use home tests for: confirmation that a solution contains peptide (as opposed to being saline alone), rough screening for very different compounds (semaglutide versus totally unrelated compound). What you cannot use them for: precise purity assessment or verification that the identity is correct.

This is the sort of thing that ought to be settled and apparently is not.

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.

The arithmetic in post #2 is right; the assumption feeding it is the part to check.

Molecular tests: DNA or RNA tests are not applicable to peptides, which do not contain nucleic acids. Peptide-specific tests rely on protein recognition, not nucleic-acid detection.

Precision of home tests: most consumer-accessible devices are not precise to the level people want ("is this 99% pure or 97% pure"). They give a yes/no or a rough category, not a quantitative number.

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.

Narrowing post #6, because the general version has more than one answer.

What physical quantity does the device measure? A colorimetric or lateral-flow method typically responds to a class of chemistry rather than to a specific molecule. It can distinguish "peptide present" from "nothing present" but generally cannot distinguish the intended peptide from a closely related one.

Adding it because I spent an afternoon working it out and nobody should have to twice.