I would put moderate confidence on the mainstream reading of quantitation and no more. That is not scepticism for its own sake; it is where the sourcing actually stops.
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Analytics · Home & field testing · continued
Coming back to: Why quantitation is the hard part, not detection posts 61–90
This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
Post #61 is right about the mechanism and I think understates the practical bit.
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.
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k.agyeman, post #32: Thank you for the correction. I would rather find out here than later. Go to post
Coming back to post #60, because the follow-up matters more than the original answer.
Nobody has said the unglamorous part of quantitation yet, so: most of the variation is explained by things that are boring to write about and easy to check.
vial_slope, post #53: Everything in post #49 holds. The case it does not cover is the one I have. Quantitation sits at the boundary between what this community can usefully discuss and what it cannot, and I think it falls on the discussable side, narrowly. Go to post
Where I have landed on quantitation, having got it wrong once in public: the direction is clear, the magnitude is not, and anyone quoting a precise magnitude has borrowed it from somewhere that did not measure it.
Confirming post #66 from a second method, which matters more than confirming it from a second person.
Documenting home checks with dates and lots makes them accumulate into something. Undocumented ones evaporate and get remembered selectively.
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Collapsed as off-topic by two members at trust level 3 or above
The question underneath quantitation is usually "how would I tell?" rather than "what is true?", and that one has a method attached to it.
Write down what you would expect to see under each hypothesis before you collect anything. If they predict the same observation, collecting it will not help.
Adding a note of thanks rather than an opinion. I did not know most of that.
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TL4_Halvorsen, post #17: Post #13 describes the usual case. This is about the unusual one. Offering a way to settle quantitation rather than another opinion about it. Two measurements, taken the same way, a fortnight apart. If the difference is within the noise, the question was not answerable at this precision. Go to post
An update on my earlier quantitation post: the pattern held for another six weeks and then stopped, which I did not predict and cannot explain.
Post #71 answers the question as asked. The question underneath it is different.
An honest declaration on quantitation: I have a prior here and it is strong enough that you should weight what I say downward. Stating it rather than hiding it.
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Lundqvist, post #10: What I can speak to on quantitation is narrow, so I will keep it narrow rather than generalising from it. Beyond that boundary I do not know. Go to post
Worth separating two things that post #71 runs together.
Where I would push back on the quantitation consensus is the confidence, not the direction. The direction looks right. The confidence is borrowed.
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.
Old habit: I write down the expected answer before I calculate it.
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Small methodological point on quantitation: repeating a measurement is cheap and resolves most of what is being argued about here at no cost to anyone.
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Understood, and I withdraw the assumption I opened with.
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ch.correia, post #18: Adding the measurement that post #16 says would settle it. 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. Go to post
Picking up post #77: that is the part I would want checked first.
Adding a null result on quantitation. I looked, carefully, and found nothing, and null results deserve posting precisely because they never are.
SHermansen, post #21: Building on post #18 rather than restating it. 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. The claim is narrower than it sounds, and deliberately so. Go to post
Everything in post #80 holds. The case it does not cover is the one I have.
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.
Same conclusion as the reply above, reached differently, which is mildly reassuring.
Wendelboe, post #59: No disagreement from me. Posting only so the question does not look ignored. Go to post
The strongest argument against my own position on quantitation, stated as well as I can state it, since nobody else has yet.
ms_holloway, post #13: Answering the question post #9 raises rather than the one it answers. My position on quantitation is current rather than settled. I have revised it once already and I expect to again, so treat it accordingly. Go to post
What I would tell a new member reading about quantitation for the first time: the confident posts are not the reliable ones, and the reliable ones are longer.
Quantitation would be much easier to settle if anyone reported the denominator. Almost nobody reports the denominator.
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The most useful thing anyone has posted about quantitation in this category was a table of what had been measured and by whom. That is what I would want again.
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