An honest declaration on forced degradation studies: I have a prior here and it is strong enough that you should weight what I say downward. Stating it rather than hiding it.
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Analytics · Method validation · continued
Forced degradation studies: designing one that is informative posts 31–60
This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
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.
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sharps_bin, post #27: That is the distinction I keep failing to hold on to. Written down now. Go to post
Post #31 answers the question as asked. The question underneath it is different.
Small methodological point on forced degradation studies: repeating a measurement is cheap and resolves most of what is being argued about here at no cost to anyone.
Worth separating two things that post #31 runs together.
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 would want to see it done twice before believing it once.
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j.restrepo, post #26: Post #25 describes the usual case. This is about the unusual one. 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. I am describing what is, rather than arguing for what should be. Go to post
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.
r.chukwu, post #14: Forced degradation under acid, base, oxidation, heat and light is how specificity is actually demonstrated. The chromatograms from that work are more informative than the release data. The reasoning is more useful than the number, which is why I have shown it. Go to post
Where I part company with post #35, and it is a narrow parting.
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.
Post #39 is the version of this I will quote in future. One addition.
The most useful single question about a method: what would it fail to detect? Every method has an answer and few documents state it.
I have deliberately not rounded that, because the rounding is where the argument starts.
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z.yildiz, post #19: Post #17 describes the usual case. This is about the unusual one. 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 would be glad to be shown a cleaner way of putting this. Go to post
Specificity: the method can distinguish the intended compound from related impurities and degradation products. Tested by comparing results on pure compounds, mixtures of compounds, and degraded samples.
Seconded. It reads as careful rather than confident, which is the right register.
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Confirming post #40 from a second method, which matters more than confirming it from a second person.
What I would tell a new member reading about forced degradation studies for the first time: the confident posts are not the reliable ones, and the reliable ones are longer.
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I had written a reply contradicting post #43 and deleted it. Here is what survived.
Forced degradation studies would be much easier to settle if anyone reported the denominator. Almost nobody reports the denominator.
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p.boateng, post #16: Appreciated. The plain phrasing does more work here than a longer post would. Go to post
Adding the measurement that post #44 says would settle 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.
sharps_bin, post #27: That is the distinction I keep failing to hold on to. Written down now. Go to post
The strongest argument against my own position on forced degradation studies, stated as well as I can state it, since nobody else has yet.
Where I part company with post #46, and it is a narrow parting.
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.
I would treat that as a working assumption and revisit it.
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Answering the question post #46 raises rather than the one it answers.
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.
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l.chevalier, post #17: Specificity is the first question: does the method separate the analyte from everything reasonably expected to be present? A method that has not been challenged with its own degradation products has not answered it. Where I would look next, rather than where I would stop. Go to post
Where a pharmacopoeial monograph exists, a method that follows it inherits a great deal of assurance. Almost nothing discussed here has one.
That is the shape of it. The detail is where I would expect to be corrected.
Collapsed as off-topic by two members at trust level 3 or above
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.
h.jansen, post #36: Forced degradation studies looks different depending on whether you are reading the primary literature or the summaries of it, and the difference is not in our favour. Go to post
Forced degradation studies came up in a thread eighteen months ago and was answered well. I cannot find it, which is itself the problem, so here is the reconstruction.
Bramley, post #13: I read post #9 twice before replying, because I had assumed the opposite. Where a pharmacopoeial monograph exists, a method that follows it inherits a great deal of assurance. Almost nothing discussed here has one. That is the honest state of it as of this week. Go to post
My position on forced degradation studies is current rather than settled. I have revised it once already and I expect to again, so treat it accordingly.
Worth separating two things that post #54 runs together.
Forced degradation under acid, base, oxidation, heat and light is how specificity is actually demonstrated. The chromatograms from that work are more informative than the release data.
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This follows post #57 rather than contradicting it.
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 reporting what happened, not recommending it.
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z.adeyemi, post #32: Fine by me. I had wanted a stronger conclusion and there is not one available. Go to post
I read post #57 twice before replying, because I had assumed the opposite.
Offering a way to settle forced degradation studies rather than another opinion about it. Two measurements, taken the same way, a fortnight apart. If the difference is within the noise, the question was not answerable at this precision.
c.adebayo, post #20: 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. The confident version of this sentence would be wrong, so here is the hedged one. Go to post
If you are new and reading this thread for the answer to forced degradation studies: the answer is conditional, the conditions are in the third reply, and the rest of the thread is worth skipping.