how much of what we believe about gradient actually comes from purity threads
Genuine question, and the title is the question: how much of what we believe about gradient actually comes from purity threads.
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.
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
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.
axis labels or the trace is decoration
What wavelength, and what was the gradient?
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Push back: a longer run is not automatically better resolution. You are trading peak width for time and the ratio is what matters.
Correction: that is a tailing factor, not a plate count. Different diagnostics for different problems.
Trace posted without axis labels — asked for a relabelled version rather than removing it.
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.
How old is the column and roughly how many injections has it seen?
Is that baseline drawn by the software or by hand?
a shoulder is not an impurity until you can resolve it
system suitability before you believe any number on the run
you cannot report to two decimals off that baseline
you cannot report to two decimals off that baseline
This is the whole methodological point of the board in one line.
Small fix — 214nm, not 210. It matters for the comparison you are making with the other run.
This. A shoulder that does not baseline-resolve is a question, not a quantity.
That is area percent, not mass percent. The trace cannot give you the second one.
reproducibility beats resolution if you only get one of them
report the method or do not report the number
integration decisions move the number more than the sample does
Retention time shifted 0.4 minutes and I assumed the worst. It was the column temperature.
two labs, two gradients, two honest answers
LC-MS for identity, UV for relative quantity
Ran a blank after a high-concentration injection and found the carryover I had been calling an impurity.
area percent is relative to what the detector saw and nothing else
the column has a history and it shows in the peak shape
- 1Carryover from a previous high-concentration injection looks exactly like a…12 comments in this branch · started by u/arne_nyberg
- 2Mass spectrometry answers identity. UV purity answers relative quantity…6 comments in this branch · started by u/endotoxin_ellie