Sample handling between despatch and injection Writing it up because I had to work it out twice and would rather nobody else did.
Trying to work out what would count as evidence on sample handling between despatch, before collecting any. This is the part I usually skip and it is the part that makes the rest useful.
If two explanations predict the same observation, observing it does not help. So: what observation would separate them?
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.
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.
If it helps: the failure mode here is usually boring rather than dramatic.
Taking the opening post at face value and following it one step further.
The arithmetic on sample handling between despatch is the easy part and it is where the errors are, which is an uncomfortable combination. Show your working and someone will catch it.
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.
Grateful for the specificity. Vague answers to this question are what sent me looking.
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 will take the caveat as seriously as the claim, which is the point of putting it there.
Post #9 answers the question as asked. The question underneath it is different.
Sample handling between despatch 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 reason sample handling between despatch 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.
The most useful single question about a method: what would it fail to detect? Every method has an answer and few documents state it.
Worth separating two things that post #12 runs together.
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.
Worth one more sentence than it usually gets.
Adding a data point of agreement rather than a data point.
Coming back to post #12, because the follow-up matters more than the original answer.
My experience of sample handling between despatch 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.
What I would want before treating sample handling between despatch as settled: the method, the sample, and whether anyone tried to find the opposite result. Two of the three are usually missing.
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.
Where a pharmacopoeial monograph exists, a method that follows it inherits a great deal of assurance. Almost nothing discussed here has one.
Answering the question post #16 raises rather than the one it answers.
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.
Small correction to my own earlier position on sample handling between despatch. I had the units the wrong way round, which changes the conclusion by an order of magnitude and therefore changes it entirely.
Adding the measurement that post #21 says would settle it.
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.
Where I part company with post #21, and it is a narrow parting.
I would put moderate confidence on the mainstream reading of sample handling between despatch and no more. That is not scepticism for its own sake; it is where the sourcing actually stops.
The question underneath sample handling between despatch 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.
On post #21 — 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.
Picking up post #25: that is the part I would want checked first.
Before the thread moves on from sample handling between despatch — 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.
The distinction between a qualified instrument and a validated method is worth keeping. Both are needed and they fail in different ways.
A single observation, in a thread that deserves better than single observations.
The confident answers on sample handling between despatch and the well-sourced answers are not the same answers, which is the most useful thing I have learned reading this category.
Reading back through the sample handling between despatch threads from last year, the same three questions come up every time and only one of them has ever been answered properly. That seems like a documentation gap rather than a knowledge gap.