This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1 · go to the accepted answer.
Accuracy: the method measures what you intend to measure. For purity methods, this is tested by spike-and-recover experiments: add a known amount of impurity to a sample and measure whether you recover the added amount.
I would call that likely rather than established.
Robustness: the method gives consistent results when minor parameters vary. Tested by deliberately varying pH, temperature, flow rate, and mobile phase composition within reasonable ranges and demonstrating that results stay within acceptance.
I read post #60 twice before replying, because I had assumed the opposite.
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.
This is the sort of thing the wiki should carry and currently does not.
Range: the concentration range over which the method has been validated. Going outside the validated range is going outside the method's demonstrated performance.
On post #64 — agreed on the reasoning, with one qualification.
Stability-indicating method: one that can separate a compound from its degradation products. Critical for assay methods that claim to measure actual degradation (as opposed to purity, which is orthogonal).
Useful. I had the fact and not the reason, which turns out to be the important half.
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.
Posted with less confidence than the sentence structure implies.
Post #68 describes the usual case. This is about the unusual one.
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.
Happy to be corrected if someone holds better data than mine.
The most useful single question about a method: what would it fail to detect? Every method has an answer and few documents state it.
Right, and stated more narrowly than I would have dared to state it.
An independent laboratory's method being different from the supplier's is not a discrepancy. It becomes one only when the results differ by more than both methods' demonstrated precision.
Small point, but it is the one that usually catches people.
Post #71 is right about the mechanism and I think understates the practical bit.
Documented validation is what separates a number from an opinion expressed numerically. That is the whole reason to ask for the procedure identifier rather than the method name.
It is one reading of the data and not the only reasonable one.
On post #71 — agreed on the reasoning, with one qualification.
Where a pharmacopoeial monograph exists, a method that follows it inherits a great deal of assurance. Almost nothing discussed here has one.
Not disagreeing with anyone above, just adding the bit I keep having to look up.
Validation is compound-specific and matrix-specific. A method validated for one peptide is a starting point for another and not a validated method for 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.
Adding a source would improve this post and I do not have one to hand.
Post #75 describes the usual case. This is about the unusual one.
Limits of detection and quantitation: LOD is the lowest concentration that produces a signal above background. LOQ is the lowest concentration at which the method meets precision and accuracy acceptance criteria. Both are determined empirically.
This has been discussed before and I could not find the thread, so, again.
Adding the measurement that post #79 says would settle it.
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.
It is worth checking rather than assuming, which costs nothing.
Answering the question post #78 raises rather than the one it answers.
Range and working range are different things and a certificate rarely distinguishes them. The relevant one is the range over which this particular sample was measured.
The general answer and the answer for your case may diverge here.
The distinction between a qualified instrument and a validated method is worth keeping. Both are needed and they fail in different ways.
Sample stability during analysis is part of validation and is routinely ignored. A preparation that degrades in the autosampler over eight hours produces a sequence-dependent result.
Taking post #85 at face value and following it one step further.
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.
Old habit: I write down the expected answer before I calculate it.
Accuracy: the method measures what you intend to measure. For purity methods, this is tested by spike-and-recover experiments: add a known amount of impurity to a sample and measure whether you recover the added amount.
I would put this at better than even and not much better.
Saving this. It is the version I will quote when the question comes round again.
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.