On the subject in the title: Relative retention time as a better inter-laboratory comparator Working notes rather than a conclusion.
What changes if the standard account of relative retention time is wrong? I ask because I have been treating it as settled and I noticed this week that I could not say why.
Working through the consequences rather than the evidence, since others here are better placed on the evidence.
The limit of quantitation determines what the impurity table can honestly contain. Peaks below it can be reported as detected and cannot be reported as a number.
I have separated what I observed from what I concluded, which does not always happen.
Picking up post #2: that is the part I would want checked first.
Reporting a result to more decimal places than the method's precision supports is a small dishonesty that appears everywhere. A method with a two per cent relative standard deviation does not support a figure quoted to a hundredth.
I would treat the number as indicative rather than as a measurement.
Precision and repeatability: within-run and between-run variability of the method. Acceptance criterion is typically a relative standard deviation of ≤2% for area measurements.
Having read the whole relative retention time 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.
Adding a data point of agreement rather than a data point.
Post #4 describes the usual case. This is about the unusual one.
Trying to state the relative retention time 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.
Building on post #6 rather than restating it.
Reporting a result to more decimal places than the method's precision supports is a small dishonesty that appears everywhere. A method with a two per cent relative standard deviation does not support a figure quoted to a hundredth.
The uncertainty is in the assumption, not in the calculation.
Relative retention time looks different depending on whether you are reading the primary literature or the summaries of it, and the difference is not in our favour.
Post #8 put the caveat in the right place and I want to underline it.
An update on my earlier relative retention time post: the pattern held for another six weeks and then stopped, which I did not predict and cannot explain.
Building on post #11 rather than restating it.
The most useful single question about a method: what would it fail to detect? Every method has an answer and few documents state it.
That has held every time I have looked, which is not the same as always.
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