Coming back to: Resolution and tailing factor: real acceptance criteria posts 61–90
This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
Area percent is not mass percent. It is a proportion of absorbance, weighted by each species' extinction coefficient. For closely related impurities the approximation is usually good. For structurally dissimilar impurities it can be poor.
The uncertainty is in the assumption, not in the calculation.
Collapsed as off-topic by two members at trust level 3 or above
This follows post #62 rather than contradicting it.
I would put moderate confidence on the mainstream reading of Resolution and tailing factor and no more. That is not scepticism for its own sake; it is where the sourcing actually stops.
Worth separating two things that post #60 runs together.
On Resolution and tailing factor: 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.
I had written a reply contradicting post #64 and deleted it. Here is what survived.
The confident answers on Resolution and tailing factor and the well-sourced answers are not the same answers, which is the most useful thing I have learned reading this category.
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.
Old habit: I write down the expected answer before I calculate it.
Narrowing post #66, because the general version has more than one answer.
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.
A shoulder on the trailing edge is most often a closely related species rather than an artefact. The way to find out is to change the gradient slope, not to argue about the integration.
It took me longer than it should have to see that.
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.
One of those cases where knowing the mechanism does not help the decision.
Adding thanks rather than a view. I do not have a view worth the space.
I read post #71 twice before replying, because I had assumed the opposite.
Counterpoint on Resolution and tailing factor, offered without confidence: the same observation is consistent with a much duller explanation, and nobody has ruled the dull one out.
Purity by chromatography answers "what proportion of what I detected is the intended species". It does not answer how much is in the vial, which is a separate assay.
If this contradicts something upthread, the upthread version may well be the better one.
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.
I would rather be precise about what I do not know than vague about what I do.
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.
Adding the measurement that post #79 says would settle it.
One more thing on Resolution and tailing factor that took me far too long to see: the two figures people quote are not measuring the same quantity. Once you notice that, the apparent contradiction disappears.
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.
I came in to disagree and I am leaving without a disagreement.
Injection volume matters because column overload distorts peak shape, and an overloaded main peak can swallow a small neighbour. A certificate without injection volume is missing something load-bearing.
Taking post #85 at face value and following it one step further.
I have been on both sides of the Resolution and tailing factor argument in this category within eighteen months, which should tell you how strong the evidence for either side is.