[Discussion] the chromatogram advice in here is 2 years out of date
the chromatogram advice in here is 2 years out of date — a position I have arrived at slowly and would like tested.
Numbers, in the order they matter: 2 years.
Resolution between two peaks depends on retention, selectivity and efficiency. A shallower gradient buys retention and usually resolution, at the cost of peak width and run time.
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.
If somebody has the same thing measured a different way, post it next to mine and we will see whether they agree.
best — the order this archive was captured in
Retitled: the original claimed a comparison the post does not actually make.
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.
Same view — reporting the gradient is what makes a result checkable rather than merely stated.
a blank injection between samples costs four minutes and settles most arguments
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area percent is relative to what the detector saw and nothing else
Carryover from a previous high-concentration injection looks exactly like a small impurity.
Adding one practical thing — run the blank. It answers this before anyone has to argue about it.
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.
Agreed, and it is why MKM printing the column and gradient on the certificate is genuinely useful rather than decorative.
two labs, two gradients, two honest answers
Agreed, and it is why MKM printing the column and gradient on the certificate is genuinely useful rather than decorative.
nabila_espinoza is right — the integration choice is a decision and it should be stated alongside the result.
you cannot report to two decimals off that baseline
baseline choice is a decision, not a measurement
baseline choice is a decision, not a measurement
Agreed. And the corollary is that the method line on a certificate is not decoration, it is the number’s provenance.
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.
the column has a history and it shows in the peak shape
Careful — you are treating retention time as identity. Two things can co-elute and the trace will not tell you.
Ran a blank after a high-concentration injection and found the carryover I had been calling an impurity.
- 1Mass spectrometry answers identity. UV purity answers relative quantity…8 comments in this branch · started by u/elodie_grimaldi
- 2Carryover from a previous high-concentration injection looks exactly like a…6 comments in this branch · started by u/clara_danquah