Spike-and-recover accuracy for a peptide assay posts 91–120
This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
I keep a log for spike-and-recover accuracy specifically because my memory of it turned out to be systematically wrong in one direction. Six weeks of notes cost nothing and settled it.
Answering the question post #89 raises rather than the one it answers.
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.
On reflection I would soften that slightly.
Collapsed as off-topic by two members at trust level 3 or above
The arithmetic in post #93 is right; the assumption feeding it is the part to check.
Before the thread moves on from spike-and-recover accuracy — what is the sample size behind the claim? I am not being difficult; I have seen the same figure quoted from an n of four and from an n of four hundred.
Where a pharmacopoeial monograph exists, a method that follows it inherits a great deal of assurance. Almost nothing discussed here has one.
The interesting part of this is the exception, and I do not understand the exception.
Adding the measurement that post #97 says would settle it.
Small correction to my own earlier position on spike-and-recover accuracy. I had the units the wrong way round, which changes the conclusion by an order of magnitude and therefore changes it entirely.
Confirming post #97 from a second method, which matters more than confirming it from a second person.
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.
Adding the boring version of spike-and-recover accuracy, 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 most useful single question about a method: what would it fail to detect? Every method has an answer and few documents state it.
Take the reasoning and check the arithmetic; I do not always get it right.
Worth separating two things that post #101 runs together.
The question underneath spike-and-recover accuracy is usually "how would I tell?" rather than "what is true?", and that one has a method attached to it.
Write down what you would expect to see under each hypothesis before you collect anything. If they predict the same observation, collecting it will not help.
Following, with nothing to contribute beyond having asked the same thing elsewhere.
My experience of spike-and-recover accuracy contradicts the reply above. I am posting it as a data point rather than as a refutation, because one person's experience is exactly that.
Narrowing post #105, because the general version has more than one answer.
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.
Spike-and-recover accuracy is well covered in the tag pages, and the older discussions are better than the recent ones because they were argued out properly. Worth twenty minutes before adding to this one.
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 have changed my mind on this once already, so take it as current rather than settled.
I had written a reply contradicting post #105 and deleted it. Here is what survived.
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).
The reason spike-and-recover accuracy keeps being re-asked is that the answer is conditional and people quote it without the condition. It is not that the answer is unknown.
Small methodological point on spike-and-recover accuracy: repeating a measurement is cheap and resolves most of what is being argued about here at no cost to anyone.
On post #110 — agreed on the reasoning, with one qualification.
The most useful single question about a method: what would it fail to detect? Every method has an answer and few documents state it.
Collapsed as off-topic by two members at trust level 3 or above
Having read the whole spike-and-recover accuracy thread before replying: the question in the first post has not actually been answered yet, and three of us have answered a nearby one instead.
No notes. Posting so the count is not one.
This follows post #114 rather than contradicting it.
Spike-and-recover accuracy is worth one more sentence than it usually gets, and the sentence is the one about how the number was arrived at.
Post #118 put the caveat in the right place and I want to underline it.
Distinguishing three things in the spike-and-recover accuracy discussion that keep getting used interchangeably: the observation, the proposed mechanism, and the recommendation that gets attached to both.