Revisiting: Sample handling between despatch and injection

Posting this under the heading it deserves: Revisiting: Sample handling between despatch and injection Everything below is what sits behind that.

Reading back through what has been written here about Sample handling between despatch, three questions come up every time and only one has ever been answered properly.

Listing all three, with what I think the state of the answer is for each, so the thread can start further along than the last one did.

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.

A guess, clearly labelled as one.

The arithmetic in the opening post is right; the assumption feeding it is the part to check.

The most useful single question about a method: what would it fail to detect? Every method has an answer and few documents state it.

For what it is worth, the same held on the two occasions I checked.

Answering the question post #2 raises rather than the one it answers.

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.

Thank you for taking the time. That was more work than a reply usually is.

Post #2 put the caveat in the right place and I want to underline it.

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.

Two sources, same conclusion, and I could not rule out that one copied the other.

Narrowing post #4, because the general version has more than one answer.

The distinction between a qualified instrument and a validated method is worth keeping. Both are needed and they fail in different ways.

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.

Taking post #8 at face value and following it one step further.

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.

Post #6 and I disagree about the size of the effect, not about the direction.

Adding a reference point for Sample handling between despatch. Mine is a single case, collected without controls, and I am posting the method alongside it so it can be discounted appropriately.