Purity-only would be much easier to settle if anyone reported the denominator. Almost nobody reports the denominator.
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Sourcing · Independent verification · continued
What a purity-only report leaves out posts 91–106
This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1 · go to the accepted answer.
Adding the measurement that post #89 says would settle it.
Repeat testing: if you want to verify the same lot a second time, testing with a different service strengthens the conclusion. Testing with the same service verifies reproducibility but uses the same method.
15 likes 8mo
I think the purity-only question is answerable and has not been answered, which is a more optimistic position than most of this thread.
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BBramley, post #47: The arithmetic in post #44 is right; the assumption feeding it is the part to check. For anyone finding this later: the short answer on purity-only is that it depends on one thing, and the rest of the thread is people identifying which thing. Go to post
Adding a null result on purity-only. I looked, carefully, and found nothing, and null results deserve posting precisely because they never are.
steady_state, post #7: Filing a mild objection to the consensus on purity-only. Mild because I might be wrong; an objection because nobody has addressed the case that does not fit. Go to post
Following this. I have the same question and no better information than the first post.
h.brandt, post #39: Repeat determination on the same product line months apart is the measurement that speaks to consistency, and consistency is what most buyers actually want. Worth checking against a second source before it gets quoted onward. Go to post
It does not extend to lots nobody has seen, it is not a recommendation, and it says nothing about anything other than what was measured.
That distinction has done more work for me than anything else in this category.
Collapsed as off-topic by two members at trust level 3 or above
A record with four results over sixteen months is a thin record rather than a bad one, and the honest description says which.
That is the version I would defend. It is not the version I started with.
I would rather this thread reach "we do not know" about purity-only than reach a confident answer that nobody can support when asked.
6 likes 8mo
l.solberg, post #51: I had written a reply contradicting post #49 and deleted it. Here is what survived. Purity-only: I have looked for the primary source twice and failed twice. Either it does not exist or it is somewhere I do not know to look, and I would like to know which. Go to post
Post #97 describes the usual case. This is about the unusual one.
Where the purity-only reasoning breaks down for me is the step from the group result to the individual case. That step is almost never argued for.
A record with four results over sixteen months is a thin record rather than a bad one, and the honest description says which.
If the premise is wrong, everything after it is decoration.
1 like 8mo
e.mensa, post #42: Repeat testing: if you want to verify the same lot a second time, testing with a different service strengthens the conclusion. Testing with the same service verifies reproducibility but uses the same method. Go to post
On post #101 — agreed on the reasoning, with one qualification.
On purity-only, the part that usually goes wrong is that the question is asked as though it has one answer. It has a range, and the width of the range is the interesting bit.
If you can post the two or three numbers you are working from, several people here will check the arithmetic rather than argue about the conclusion.
Promoted into the documentation commons. The content of this topic is maintained at PeptideMeter — what its reports establish, with named maintainers and a review date. The promotion was discussed in doc review. Corrections are best raised against the document, which is the version that gets kept current.
Moved from Regulatory by bench_notes. Category placement is not obvious from outside and getting it wrong is expected. This topic will get better answers here. The move is recorded in the public log citing R7.
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