Posting this under the heading it deserves: Spike-and-recover accuracy for a peptide assay Everything below is what sits behind that.
Asking about spike-and-recover accuracy on behalf of the question I keep seeing asked badly, including by me.
Framed properly it is answerable. Framed the usual way it is not, and that is most of why the previous threads went nowhere.
On spike-and-recover accuracy: the maintained page in the documentation commons covers the general case with citations and a review date, which is more reliable than any reply here including this one.
Post #2 describes the usual case. This is about the unusual one.
Answering the spike-and-recover accuracy question as asked, then the question I think is meant. As asked: yes, with the qualification below. As meant: it depends on how the first measurement was taken.
Post #4 is right about the mechanism and I think understates the practical bit.
Where a pharmacopoeial monograph exists, a method that follows it inherits a great deal of assurance. Almost nothing discussed here has one.
The step people skip is the one I have spelled out.
What I would want before treating spike-and-recover accuracy as settled: the method, the sample, and whether anyone tried to find the opposite result. Two of the three are usually missing.
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 would put a moderate confidence on that and no more.
Noted, and thank you for writing it out rather than summarising it.
Confirming post #9 from a second method, which matters more than confirming it from a second person.
Summarising the spike-and-recover accuracy thread so far, since it is long and the answer is buried: the first reply has the method, the fourth has the correction to it, and the rest is people agreeing at length.
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.
Post #13 is right about the mechanism and I think understates the practical bit.
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 am describing what is, rather than arguing for what should be.
Adding a null result on spike-and-recover accuracy. I looked, carefully, and found nothing, and null results deserve posting precisely because they never are.
Post #19 is right about the mechanism and I think understates the practical bit.
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.
Anyone with a larger sample, please post it.
My position on spike-and-recover accuracy is current rather than settled. I have revised it once already and I expect to again, so treat it accordingly.
I read post #24 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.
The right answer here may simply be that it has not been measured.
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.
The most useful reply I ever got about spike-and-recover accuracy was a request to state my units. It sounds like pedantry and it has saved me twice.
Counterpoint on spike-and-recover accuracy, offered without confidence: the same observation is consistent with a much duller explanation, and nobody has ruled the dull one out.