Why quantitation is the hard part, not detection

Why quantitation is the hard part, not detection I have a specific reason for asking rather than idle curiosity, and the context is below.

Collecting what is known about quantitation in one place, because it is currently spread across a category, two tag pages and a thread that is hard to find.

This is a summary rather than new work, and I have attributed each part to where I found it.

Picking up the opening post: that is the part I would want checked first.

Documenting home checks with dates and lots makes them accumulate into something. Undocumented ones evaporate and get remembered selectively.

Flagging that the sources on this are thinner than the confidence in the thread suggests.

Source for the quantitation figure, since it was asked for. It is in the discussion rather than the abstract, which is why the version circulating is stronger than the paper is.

Reading the surrounding paragraph is worth the two minutes. The authors are more careful than their summarisers.

A request rather than an answer: could whoever has the primary source for quantitation post it? I have seen the claim three times this month and each version had lost a qualifier.

The right question for any home test is: what physical quantity does it measure, and what would have to be true for that quantity to answer your question? Most disappointment comes from skipping it.

I disagree with the framing of quantitation above, and I think it is a substantive disagreement rather than a terminological one. Setting out why, so it can be checked.

The reasoning depends on an assumption that is doing a lot of work and is never stated. If the assumption holds, the conclusion follows. I do not think it holds generally.

No disagreement from me. Posting only so the question does not look ignored.

Quantitation is one of those subjects where the general answer and the answer for a specific case diverge, and the thread will go in circles until someone says which one is being asked for.

Ultraviolet absorbance at 280 nanometres estimates concentration for peptides containing aromatic residues and gives nothing for peptides that do not. Knowing which yours is comes first.

I keep a log for quantitation specifically because my memory of it turned out to be systematically wrong in one direction. Six weeks of notes cost nothing and settled it.

Taking post #10 at face value and following it one step further.

The claim about quantitation upthread is stronger than its source supports. I have read the source. The source says "associated with" and the post says "causes".

Post #8 and I disagree about the size of the effect, not about the direction.

A home refractometer is not measuring what people hope it is measuring in these preparations, and the readings are dominated by everything other than the peptide.

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

Research-use-only material is not certified for anything by anybody, and no home procedure changes that. What home checks buy you is early detection of the obvious problems.

Quantitation: I would want to see the raw numbers rather than the summary before agreeing. Summaries lose exactly the information that would settle this.