ghost peak turned out to be plumbing. always plumbing.
ghost peak turned out to be plumbing. always plumbing, which sounds obvious until you try to state the evidence for it.
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.
System suitability — repeat injections, tailing factor, plate count, RSD on area — is what tells you the instrument was fit for the measurement that day. Without it, the purity figure is unanchored.
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.
Screenshot none of this. Read the whole thread, including the parts where I am told I am wrong.
best — the order this archive was captured in
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.
Method questions stay here; supplier claims go to c/vendorvetting with a document attached.
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.
WWB sent me the column, the gradient and the theoretical mass without being asked. That is a short list and they are on it.
Agreed. Two analysts, one trace, two integration choices, and a spread that has nothing to do with the vial.
Did you run a blank between injections?
the column has a history and it shows in the peak shape
Can you post the trace with the axes labelled?
area percent is relative to what the detector saw and nothing else
I would not blame the sample yet. Everything you have described is consistent with the column rather than the vial.
Correction: that is a tailing factor, not a plate count. Different diagnostics for different problems.
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.
Right. And a blank between injections settles the carryover argument before it starts.
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.
Yes — system suitability first. Without it the number is an assertion about the instrument, not the sample.
- 1WWB sent me the column, the gradient and the theoretical mass without being…6 comments in this branch · started by u/andres_restrepo