[PSA] HPLC is not what most of this community thinks it is
HPLC is not what most of this community thinks it is. It comes up every few weeks and the answer has not changed.
A shoulder that does not baseline-resolve cannot be quantified honestly. You can report it as an unresolved shoulder, which is useful information, or you can develop the method until it resolves.
Chased a ghost peak for three weeks. It was the plumbing. It is always the plumbing.
Carryover from a previous high-concentration injection looks exactly like a small impurity. The blank injection is four minutes and it removes the ambiguity entirely.
Corrections welcome, especially the pedantic ones. Pedantry is how this board earns its reputation.
best — the order this archive was captured in
Area percent is the integrated area of your peak over the total integrated area at one wavelength on one gradient. Change any of those and the number changes without the sample changing.
Right. And a blank between injections settles the carryover argument before it starts.
Gave the same trace to two people I trust and got two integrations about a point apart. That was the most educational afternoon I have had here.
baseline choice is a decision, not a measurement
UV response is not uniform across species. At 214nm you are looking at the peptide bond, which is why it is the working wavelength for this class; at 280nm you only see tryptophan, tyrosine and phenylalanine.
area percent is relative to what the detector saw and nothing else
Yes — system suitability first. Without it the number is an assertion about the instrument, not the sample.
Mass spectrometry answers identity. UV purity answers relative quantity under the run conditions. A document with one and not the other is answering half the question, and the half it answers should be stated.
Mass spectrometry answers identity.
This is the whole methodological point of the board in one line.
reproducibility beats resolution if you only get one of them
reproducibility beats resolution if you only get one of them
Adding one practical thing — run the blank. It answers this before anyone has to argue about it.
- 1UV response is not uniform across species. At 214nm you are looking at the…6 comments in this branch · started by u/niels_lindqvist