Reflectance and photometric devices: precision in practice — a second dataset — setting out what I have, and where I think it stops being reliable.
Posting a small dataset on Reflectance and photometric devices. It is mine, it is uncontrolled, and the method is stated so it can be discounted appropriately.
What I would like is not agreement but a second dataset collected by someone with no stake in mine. If one exists I would rather read it than argue for this one.
Adding a data point of agreement rather than a data point.
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.
The most useful home practice is not a test at all: photograph the vial, the cake, the label and the document on arrival. It costs nothing and it is the evidence you will wish you had.
Post #3 and I disagree about the size of the effect, not about the direction.
The reason Reflectance and photometric devices is hard to answer is that the obvious measurement and the relevant quantity are not the same thing, and substituting one for the other is silent.
Taking post #3 at face value and following it one step further.
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.
I would be interested in a counterexample if anyone has one.
An observation about Reflectance and photometric devices that I cannot explain and am posting anyway, on the principle that unexplained observations are more useful public than private.
My understanding of Reflectance and photometric devices is a few years old and may have been superseded. If it has been, I would genuinely like to know rather than keep repeating 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.
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.
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.
Worth separating Reflectance and photometric devices as a question about the compound from Reflectance and photometric devices as a question about the documentation. They get answered by different people and only one of them is answerable here.
Picking up post #12: 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.
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.
Coming back to post #14, because the follow-up matters more than the original answer.
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.
This follows post #16 rather than contradicting it.
For anyone finding this later: the short answer on Reflectance and photometric devices is that it depends on one thing, and the rest of the thread is people identifying which thing.
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.
Post #20 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.
Anyone with a larger sample, please post it.
I would call the community position on Reflectance and photometric devices likely rather than established, and I would be comfortable defending that hedge.
Lateral-flow devices: like a rapid COVID test. They have a reagent strip and produce a colour result. They are quick but not precise and not intended for quantitative work.
I am describing what is, rather than arguing for what should be.
Everything in post #23 holds. The case it does not cover is the one I have.
Counterpoint on Reflectance and photometric devices, offered without confidence: the same observation is consistent with a much duller explanation, and nobody has ruled the dull one out.
Narrowing post #23, because the general version has more than one answer.
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.
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.
Answering the question post #27 raises rather than the one it answers.
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.
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.
Happy to expand any of that if it is the useful part.