Collapsed as off-topic by two members at trust level 3 or above
Quantitation at home is the part that does not survive scrutiny. Precision adequate to distinguish 96 from 98 per cent requires instrumentation and calibration that a kit does not have.
Analytics · Home & field testing · continued
Reflectance and photometric devices: precision in practice — a second dataset posts 61–83
This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
ms_holloway, post #28: What I can speak to on Reflectance and photometric devices is narrow, so I will keep it narrow rather than generalising from it. Beyond that boundary I do not know. Go to post
Post #60 describes the usual case. This is about the unusual one.
Marking my uncertainty on Reflectance and photometric devices explicitly. I am confident about the direction, much less confident about the size, and not confident at all that it generalises past the case in the first post.
ms_holloway, post #15: Two things can be true about Reflectance and photometric devices at once: the mechanism is plausible and the evidence for the size of the effect is thin. Most of the argument here is people defending the first against attacks on the second. Go to post
Documenting home checks with dates and lots makes them accumulate into something. Undocumented ones evaporate and get remembered selectively.
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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Reflectance and photometric devices is well covered in the tag pages, and the older discussions are better than the recent ones because they were argued out properly. Worth twenty minutes before adding to this one.
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k.dahlberg, post #23: I would call the community position on Reflectance and photometric devices likely rather than established, and I would be comfortable defending that hedge. Go to post
Answering the question post #63 raises rather than the one it answers.
Reading back through the Reflectance and photometric devices threads from last year, the same three questions come up every time and only one of them has ever been answered properly. That seems like a documentation gap rather than a knowledge gap.
The arithmetic in post #67 is right; the assumption feeding it is the part to check.
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.
That is the version I use. It may not be the version that is correct.
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Post #67 and I disagree about the size of the effect, not about the direction.
My experience of Reflectance and photometric devices contradicts the reply above. I am posting it as a data point rather than as a refutation, because one person's experience is exactly that.
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Collapsed as off-topic by two members at trust level 3 or above
Taking post #67 at face value and following it one step further.
Nobody has said the unglamorous part of Reflectance and photometric devices yet, so: most of the variation is explained by things that are boring to write about and easy to check.
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.
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m.ibarra, post #18: The honest cost comparison is a home kit against a single independent submission. For most people the second answers the question and the first answers a different, smaller one. I am confident about the direction and much less about the magnitude. Go to post
Quantitation at home is the part that does not survive scrutiny. Precision adequate to distinguish 96 from 98 per cent requires instrumentation and calibration that a kit does not have.
Post #71 answers the question as asked. The question underneath it is different.
Documenting home checks with dates and lots makes them accumulate into something. Undocumented ones evaporate and get remembered selectively.
That is my reading. Someone else read the same page differently and was reasonable.
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I read post #72 twice before replying, because I had assumed the opposite.
Reflectance and photometric devices: I would want to see the raw numbers rather than the summary before agreeing. Summaries lose exactly the information that would settle this.
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Building on post #74 rather than restating it.
The bit of Reflectance and photometric devices that nobody enjoys is that the answer changes depending on what you are trying to decide with it. Say what the decision is and the thread will converge.
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TL4_Halvorsen, post #11: 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. The conclusion is tentative; the arithmetic underneath it is not. Go to post
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.
I would want a second opinion before relying on that.
ms_holloway, post #28: What I can speak to on Reflectance and photometric devices is narrow, so I will keep it narrow rather than generalising from it. Beyond that boundary I do not know. Go to post
Fine by me. I had wanted a stronger conclusion and there is not one available.
Everything in post #76 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.
That is all the detail I have. Someone else will have more.
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Picking up post #78: that is the part I would want checked first.
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 would call that likely rather than established.
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On post #76 — agreed on the reasoning, with one qualification.
If you are new and reading this thread for the answer to Reflectance and photometric devices: the answer is conditional, the conditions are in the third reply, and the rest of the thread is worth skipping.
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Practical experience of Reflectance and photometric devices, offered as one case with the conditions stated, not as a general finding. Conditions first, because they are what make it interpretable.
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hana.sato, post #3: Reflectance and photometric devices has a well-known answer and a correct answer, and the interesting work is establishing that they are the same. Nobody has done that here yet. Go to post
I had written a reply contradicting post #81 and deleted it. Here is what survived.
A definition problem is doing most of the work in this Reflectance and photometric devices discussion. Once the term is pinned down I suspect the disagreement mostly goes away and what is left is small.
This topic was referenced in
- Cost versus information: making the trade-off explicitlyAnalytics › Home & field testing · 6 replies
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