Posting this under the heading it deserves: Second pass at: Identical chromatograms across two different lots Everything below is what sits behind that.
Something about Identical chromatograms does not reconcile and I would like a second pair of eyes before I decide which half is wrong.
Two sources, both reputable, giving figures that cannot both be right unless they are measuring different quantities. My suspicion is that they are, and I cannot see how.
I read the opening post twice before replying, because I had assumed the opposite.
Small methodological point on Identical chromatograms: repeating a measurement is cheap and resolves most of what is being argued about here at no cost to anyone.
This follows the opening post rather than contradicting it.
Prices well below the rest of the market are a fact rather than a finding. They are worth noting and they do not establish anything on their own.
Keep the two claims separate. "The result on this lot did not match the certificate" is a report that can be checked. "This supplier is dishonest" is an allegation about intent and nothing in a chromatogram supports it.
I have said this before in a thread nobody could find, so it is worth repeating.
An honest declaration on Identical chromatograms: I have a prior here and it is strong enough that you should weight what I say downward. Stating it rather than hiding it.
This settles it for me, at least until somebody posts a reason it should not.
Taking post #4 at face value and following it one step further.
A document with no method identification is not evidence of anything wrong. It is evidence that the document cannot be checked, which is a different and weaker statement.
Post #7 and I disagree about the size of the effect, not about the direction.
Having read the whole Identical chromatograms thread before replying: the question in the first post has not actually been answered yet, and three of us have answered a nearby one instead.
Careful with the language on Identical chromatograms. "Not detected" and "not present" are different findings and the first is a statement about the method.
Post #9 is right about the mechanism and I think understates the practical bit.
Identical chromatograms: 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.
Where somebody posts a concern, ask what would resolve it before arguing about it. Half of these threads end with a document nobody had asked for.
That is the shape of it. The detail is where I would expect to be corrected.
Two questions I would want answered before drawing anything from the Identical chromatograms data above: how were the cases selected, and what happened to the ones that dropped out.
The practical version of Identical chromatograms is three sentences long. The rigorous version is three pages and reaches the same conclusion with the conditions attached.
Post #13 and I disagree about the size of the effect, not about the direction.
Where I would push back on the Identical chromatograms consensus is the confidence, not the direction. The direction looks right. The confidence is borrowed.
The most useful contribution to this subcategory is a resolved case written up with the resolution, because the unresolved ones are all anyone remembers.
Written quickly, so the reasoning may be tighter than the wording.
Everything in post #17 holds. The case it does not cover is the one I have.
One caution on Identical chromatograms: everything above assumes the underlying documentation is what it claims to be. That assumption is doing real work and is rarely stated.
For anyone finding this later: the short answer on Identical chromatograms is that it depends on one thing, and the rest of the thread is people identifying which thing.
The guidelines draw that line for a practical reason as much as a fair one: reports accumulate into something useful and allegations do not.
Caveat: everything above assumes the paperwork is what it says it is.
The arithmetic in post #21 is right; the assumption feeding it is the part to check.
Two things can be true about Identical chromatograms 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.
Helpful, and short, which on this subject is harder than long.
Adding the boring version of Identical chromatograms, because the interesting version keeps getting posted and the boring one is usually right.
Check the ordinary explanations, in order, and stop when one of them accounts for what you are seeing. Most of the time the second one does.
The strongest single signal available cheaply is what happens when you ask a technical question. A quantitative answer inside a working day is difficult to fake at scale.
That is all I can say without guessing.
Pricing patterns: unusually low prices for what are otherwise consistent with market rates might indicate lower quality, stolen goods, or a scam. Unusually high prices without justification raise different flags.
The step people skip is the one I have spelled out.
Post #25 describes the usual case. This is about the unusual one.
A stock listing that never changes and a lead time that never varies are both worth noticing. Real operations have variation in them.
The conclusion is tentative; the arithmetic underneath it is not.
This follows post #26 rather than contradicting it.
Small correction to my own earlier position on Identical chromatograms. I had the units the wrong way round, which changes the conclusion by an order of magnitude and therefore changes it entirely.
Worth separating two things that post #28 runs together.
The question underneath Identical chromatograms 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.