Coming back to the opening post, because the follow-up matters more than the original answer.
The most useful single question about a method: what would it fail to detect? Every method has an answer and few documents state it.
The answer changed when I changed how I was measuring, which was informative.
Robustness testing deliberately varies the parameters most likely to drift — organic percentage, pH, temperature, flow — and shows the result does not. It is the part of validation that predicts whether a method will transfer.
Take it as a starting point and not as a specification.
Worth separating two things that post #61 runs together.
Adding the boring version of Validating a method, 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 useful distinction on Validating a method is between what was measured and what was inferred from it. Both end up in the same sentence and only one of them has error bars.
Post #72 answers the question as asked. The question underneath it is different.
Checked the Validating a method claim against the primary source this morning. It survives, with a narrower scope than the version quoted here. Posting the narrower scope.
Why two laboratories may disagree: after validating the same method, they may still report different purity on the same sample due to integration differences, column age differences, subtle differences in mobile phase pH or temperature. This is normal and not a sign that one is wrong.
I had written a reply contradicting post #124 and deleted it. Here is what survived.
A stability-indicating method is one demonstrated to resolve the analyte from its degradation products, usually through forced degradation. Calling a method stability-indicating without that work is a claim rather than a property.
Picking up post #131: that is the part I would want checked first.
Forced degradation studies: deliberately stress the material with acid, base, oxidant, heat, light to generate degradation products and demonstrate that the method can separate them from the parent peak. Acceptance is that the method is stability-indicating.
Stating my assumptions rather than smuggling them in.
Read the full topic (149 posts)
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