Posting this under the heading it deserves: Resolution and tailing factor: real acceptance criteria Everything below is what sits behind that.
Reading back through what has been written here about Resolution and tailing factor, 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.
On integration: where the baseline is drawn matters more than most people realise. On a clean chromatogram with well-resolved peaks the choice is inconsequential. On a chromatogram with a trailing shoulder or a rising baseline it matters. Differences of one to two percentage points between defensible integrations are ordinary.
The general answer and the answer for your case may diverge here.
Useful. I had the fact and not the reason, which turns out to be the important half.
Narrowing post #4, because the general version has more than one answer.
Having read the whole Resolution and tailing factor 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.
Everything in post #2 holds. The case it does not cover is the one I have.
Where the baseline is drawn is the least documented and most consequential choice in the whole determination. Valley-to-valley, tangent skim and forced-to-zero can span a couple of percentage points on the same chromatogram.
A shallow gradient resolves close-eluting species that a steep one merges. Two honest laboratories running different gradients can report genuinely different purities on the same vial.
Posted with less confidence than the sentence structure implies.
Typical suitability criteria are a replicate area relative standard deviation below about two per cent, a tailing factor inside a defined window, a resolution minimum against a specified peak, and a plate-count floor.
The short version is the first sentence; the rest is why.
Resolution and tailing factor sits at the boundary between what this community can usefully discuss and what it cannot, and I think it falls on the discussable side, narrowly.
Grateful for the specificity. Vague answers to this question are what sent me looking.
The arithmetic in post #9 is right; the assumption feeding it is the part to check.
Mobile-phase preparation is a genuine source of between-laboratory variation. Acid concentration and organic modifier both shift retention, and neither is usually specified to the precision that would matter.
I would want to see it done twice before believing it once.
Particle size and column dimensions determine what resolution is achievable at all. A 5 micrometre 250 millimetre column and a sub-2 micrometre 100 millimetre column are different instruments in practice.
This is the sort of thing that ought to be settled and apparently is not.
I had written a reply contradicting post #13 and deleted it. Here is what survived.
Where the Resolution and tailing factor discussion usually stalls is that nobody wants to say "I do not know" and everyone is willing to say "it varies". Those are the same sentence with different clothes on.
System suitability is not paperwork. If the replicate injections failed, the run did not happen — the numbers from it are uninterpretable rather than approximate.
Right, and stated more narrowly than I would have dared to state it.
A chromatogram image at a resolution where you can see peak shape but not baseline detail is worth having and is not the same as the data. Ask for the integration table if the number matters.
The conclusion is tentative; the arithmetic underneath it is not.
Resolution and tailing factor is a good example of a question where the honest answer is boring and the interesting answers are unsupported. I would go with boring.
This follows post #22 rather than contradicting it.
Area percent is a proportion of absorbance, not a proportion of mass. Two species with different extinction coefficients at the detection wavelength contribute unequally to the total, and nothing on the certificate corrects for that.
Method validation is the demonstration that a method can separate the compound from its degradation products and impurities reliably. A method that cannot resolve an impurity from the parent peak will not detect that impurity.
Adding the caveat now so it does not have to be extracted later.
The version of Resolution and tailing factor that circulates here is a simplification of a simplification. It is not wrong, but it has lost the conditions under which it holds, and those conditions are where the interesting cases live.
Column chemistry and particle size: smaller particles (1.7 μm) give better resolution and higher efficiency than larger particles (3.5 μm or 5 μm), at the cost of higher back pressure. Newer methods increasingly use smaller particles.
Post #25 and I disagree about the size of the effect, not about the direction.
Practical answer on Resolution and tailing factor, since the theoretical one is upthread: do the simplest check first, write down the result, and only then decide whether the complicated explanation is needed. It usually is not.
Post #26 is the version of this I will quote in future. One addition.
Genuine question rather than a rhetorical one: has anyone here actually observed Resolution and tailing factor, as opposed to read about it? The thread is long and I cannot tell.
Where I part company with post #28, and it is a narrow parting.
System suitability testing: injections run before and during the sample run to establish whether the instrument, column and method were performing when the sample was analysed. If suitability did not pass, the sample results from that run are uninterpretable.
This is the version I would want a new member to read first.