This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
Detection wavelength: 214 nm detects the peptide bond and is relatively insensitive to composition. 280 nm detects aromatic residues and is strongly composition-dependent. Area percent at one wavelength is not area percent at the other.
The general answer and the answer for your case may diverge here.
Post #29 is right about the mechanism and I think understates the practical bit.
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.
Adding this to the thread rather than to the wiki, because I am not confident enough for the wiki.
I would put moderate confidence on the mainstream reading of detection wavelength and no more. That is not scepticism for its own sake; it is where the sourcing actually stops.
Following this. I have the same question and no better information than the first post.
Trifluoroacetic acid at 0.1 per cent is the near-universal ion-pairing additive for this work, and it also raises the baseline at 214 nanometres. That is why the same sample looks noisier at low wavelength.
The uncertainty is in the assumption, not in the calculation.
On post #33 — agreed on the reasoning, with one qualification.
Where I have landed on detection wavelength, having got it wrong once in public: the direction is clear, the magnitude is not, and anyone quoting a precise magnitude has borrowed it from somewhere that did not measure it.
Adding the boring version of detection wavelength, because the interesting version keeps getting posted and the boring one is usually right.
Check the ordinary explanations, in order, and stop when one of them accounts for what you are seeing. Most of the time the second one does.
I would keep detection wavelength and the decision it usually gets used for separate in this thread. They are related and they are not the same question, and merging them is why the last one went badly.
Post #40 and I disagree about the size of the effect, not about the direction.
Detection wavelength looks different depending on whether you are reading the primary literature or the summaries of it, and the difference is not in our favour.
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.
On reflection I would soften that slightly.
Where I would push back on the detection wavelength consensus is the confidence, not the direction. The direction looks right. The confidence is borrowed.
That is a fair summary of where the discussion has got to.
Post #44 put the caveat in the right place and I want to underline it.
An honest declaration on detection wavelength: I have a prior here and it is strong enough that you should weight what I say downward. Stating it rather than hiding it.
Confirming post #46 from a second method, which matters more than confirming it from a second person.
Gradient delay volume differs between instruments and shifts the whole chromatogram. It is why a transferred method rarely reproduces retention times exactly on a different system.
Not disagreeing with anyone above, just adding the bit I keep having to look up.
Adding what did not work for me on detection wavelength, since the failures never get written up and they are half the useful information.
Thank you for the correction. I would rather find out here than later.
Post #51 put the caveat in the right place and I want to underline it.
Change the wavelength and the proportions change even though the sample has not. That is the reason the wavelength has to be on the document for the number to mean anything.
Building on post #51 rather than restating it.
Detection at 214 nanometres sees the peptide bond and therefore sees almost everything peptidic. At 280 it sees aromatic residues, so a peptide without tryptophan or tyrosine will look very different or not appear at all.
If two laboratories disagree by more than two or three percentage points, work through method, integration, sample handling, whether it was the same lot and the same vial, and whether suitability passed. After all five, a gap needs an explanation.
Noting that the question and the thing people usually mean by it are different.
Post #55 is the version of this I will quote in future. One addition.
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.
Following, with nothing to contribute beyond having asked the same thing elsewhere.
Post #58 answers the question as asked. The question underneath it is different.
Before anything else: what was the gradient, and at what wavelength? Area percent at different wavelengths is not the same number even on the same sample because different species absorb differently at different wavelengths. With the method stated, I can tell you something useful. Without it, all I can say is that there is one large peak.
It took me longer than it should have to see that.