Robustness: the parameters worth deliberately varying

Coming back to the opening post, because the follow-up matters more than the original answer.

Genuine question rather than a rhetorical one: has anyone here actually observed robustness, as opposed to read about it? The thread is long and I cannot tell.

The arithmetic in post #9 is right; the assumption feeding it is the part to check.

The most useful single question about a method: what would it fail to detect? Every method has an answer and few documents state it.

Building on post #10 rather than restating it.

Robustness 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.

The distinction between a qualified instrument and a validated method is worth keeping. Both are needed and they fail in different ways.

That is my reading. Someone else read the same page differently and was reasonable.

Fine by me. I had wanted a stronger conclusion and there is not one available.

Post #30 put the caveat in the right place and I want to underline it.

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.

My position on robustness is current rather than settled. I have revised it once already and I expect to again, so treat it accordingly.

Nothing to add, except that this is the answer I would give if asked.