On the subject in the title: Reused chromatograms across lots: how to spot it Working notes rather than a conclusion.
Something about reused chromatograms across lots 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.
The opening post put the caveat in the right place and I want to underline it.
I would keep reused chromatograms across lots and the decision it usually gets used for separate in this thread. They are related and they are not the same question, and merging them is why the last one went badly.
Reused chromatograms across lots looks different depending on whether you are reading the primary literature or the summaries of it, and the difference is not in our favour.
Having read the whole reused chromatograms across lots 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.
An honest declaration on reused chromatograms across lots: I have a prior here and it is strong enough that you should weight what I say downward. Stating it rather than hiding it.
Post #4 describes the usual case. This is about the unusual one.
A chromatogram supplied as a small image is legible for peak shape and not for baseline detail. That is enough to sanity-check an integration and not enough to reproduce it.
Two sources, same conclusion, and I could not rule out that one copied the other.
Trying to state the reused chromatograms across lots position in a way that someone who disagrees would recognise as fair, because I do not think the version in this thread passes that test.
Reused chromatograms across lots 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.
The arithmetic in post #11 is right; the assumption feeding it is the part to check.
I changed my mind about reused chromatograms across lots after someone here asked me for the source and I could not produce one. That is worth saying out loud because it is the ordinary way it happens.
Post #11 put the caveat in the right place and I want to underline it.
Two claims get bundled together under reused chromatograms across lots and they need separating. The descriptive one — this is what was observed — is usually well supported. The causal one — this is why — usually is not.
Almost every disagreement in threads like this one dissolves once you say which of the two you are making.
An itemised related-substances table with retention times says considerably more about the synthesis than a single total. A total tells you how much is not the main peak and nothing about what it is.
I am aware this is the third time this month I have made this point.
Source for the reused chromatograms across lots figure, since it was asked for. It is in the discussion rather than the abstract, which is why the version circulating is stronger than the paper is.
Reading the surrounding paragraph is worth the two minutes. The authors are more careful than their summarisers.
Where I part company with post #15, and it is a narrow parting.
Speaking only to reused chromatograms across lots as I have actually seen it, rather than as it is usually described: the effect is real, it is smaller than the thread suggests, and the variance between people is larger than the effect.
I read post #15 twice before replying, because I had assumed the opposite.
The distinction between release testing and characterisation is one industrial documents make and retail ones usually do not. It is the difference between "we tested every lot for this" and "we established this once".
That matches what I was told, which is not the same as knowing it.
Reused chromatograms across lots is one of those subjects where the general answer and the answer for a specific case diverge, and the thread will go in circles until someone says which one is being asked for.
Reused chromatograms across lots is a good example of a question where the honest answer is boring and the interesting answers are unsupported. I would go with boring.
Adding the measurement that post #20 says would settle it.
An itemised related-substances table with retention times says considerably more about the synthesis than a single total. A total tells you how much is not the main peak and nothing about what it is.
A chromatogram supplied as a small image is legible for peak shape and not for baseline detail. That is enough to sanity-check an integration and not enough to reproduce it.
The arithmetic in post #24 is right; the assumption feeding it is the part to check.
The number people quote for reused chromatograms across lots is a central estimate presented without its interval, and the interval is wide enough that the estimate is nearly uninformative on its own.
Post #26 put the caveat in the right place and I want to underline it.
On reused chromatograms across lots the community has more anecdote than the confidence in this thread implies, and I include my own contribution in that.