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.
The version of Validating a method that I was taught turned out to be a teaching simplification. Useful, and not true in the way I had assumed it was.
I read post #88 twice before replying, because I had assumed the opposite.
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.
A method transferred between laboratories needs a demonstration that it performs equivalently, not just a document describing it. Transfer is where a great many between-laboratory disagreements originate.
I would call that likely rather than established.
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.
Correct me on the arithmetic if it is wrong; I would rather know.
Narrowing post #94, because the general version has more than one answer.
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.
Everything in post #92 holds. The case it does not cover is the one I have.
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.
None of the above is medical advice and I am not qualified to give any.
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 general case is well covered; this is the awkward specific one.
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.
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.
Not a strong opinion, just a consistent one.
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.
That is the shape of it. The detail is where I would expect to be corrected.
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.
Narrowing post #100, because the general version has more than one answer.
Transfer between laboratories: a method can be transferred from one lab to another, but the receiving lab needs to demonstrate that they can achieve the same performance. This requires comparative testing and sometimes small method refinements.
Genuinely open to being wrong about this one.
My understanding of Validating a method is a few years old and may have been superseded. If it has been, I would genuinely like to know rather than keep repeating it.
Taking post #104 at face value and following it one step further.
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.
Caveat: everything above assumes the paperwork is what it says it is.
Post #103 and I disagree about the size of the effect, not about the direction.
System suitability is the ongoing evidence that a validated method is still performing. Validation is done once; suitability is done every run, and it is the one that appears on a certificate.
I am confident about the direction and much less about the magnitude.
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.
I would want to see it done twice before believing it once.
A method transferred between laboratories needs a demonstration that it performs equivalently, not just a document describing it. Transfer is where a great many between-laboratory disagreements originate.
Sensible. I would want the same detail before I acted on it either.
I read post #110 twice before replying, because I had assumed the opposite.
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.
It took me longer than it should have to see that.
Linearity across the working range is a routine demonstration and it constrains how far a result can be extrapolated. A method linear from 80 to 120 per cent of nominal says nothing about a sample at ten per cent.
That is the distinction I keep failing to hold on to. Written down now.
Everything in post #112 holds. The case it does not cover is the one I have.
Range: the concentration range over which the method has been validated. Going outside the validated range is going outside the method's demonstrated performance.
Adding the caveat now so it does not have to be extracted later.
Narrowing post #115, because the general version has more than one answer.
I would keep Validating a method 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.
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.
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).
I would want the raw data before agreeing with my own summary of it.
The arithmetic in post #117 is right; the assumption feeding it is the part to check.
A method that reports the same number for every lot is worth a second look. Real processes vary, and a total absence of variation is a statement about the measurement rather than the process.
One more caveat and then I will stop qualifying: the sample selected itself.