[PSA] chromatogram is not what most of this community thinks it is
chromatogram is not what most of this community thinks it is. Two minutes of reading now saves an argument later.
Started reporting my own integrations with the baseline choice stated. Arguments in my threads dropped by about half.
Reading a trace posted here, in the order I actually look at things.
Axes first — if the wavelength and the time axis are not labelled, I stop. Then the baseline: where has it been drawn, and does the drawing absorb anything. Then peak shape: fronting, tailing, a shoulder that never resolves. Then the blank, if one was run, for carryover.
Only after all of that do I look at the percentage, and by then I usually know how much weight it deserves. The number is the last thing on the page and the first thing everybody argues about, which is exactly backwards.
The system suitability argument, since it comes up whenever somebody posts a number without one.
Before the sample result means anything, the instrument has to be shown to be fit that day: replicate injections with an acceptable RSD on area, a tailing factor inside limits, adequate plate count, and a resolution check between the pair you care about.
None of that is exotic and all of it is routine in a laboratory that reports for a living. Its absence does not mean a number is wrong; it means the number is unanchored, and unanchored numbers should not be quoted to two decimal places on this board.
Would rather be corrected in public than confident in private.
best — the order this archive was captured in
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.
two labs, two gradients, two honest answers
reproducibility beats resolution if you only get one of them
That is area percent, not mass percent. The trace cannot give you the second one.
a shoulder is not an impurity until you can resolve it
Same method at both labs, or two different gradients?
report the method or do not report the number
area percent is relative to what the detector saw and nothing else
Trace posted without axis labels — asked for a relabelled version rather than removing it.
Disagree. Inter-lab spread of a point or two on this assay is ordinary and calling it a discrepancy misleads people.
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.
Did you run a blank between injections?
214nm sees the peptide bond, 280nm sees the aromatics
- 1A shoulder that does not baseline-resolve cannot be quantified honestly. You…8 comments in this branch · started by u/hana_lehtinen
- 2Trace posted without axis labels — asked for a relabelled version rather…6 comments in this branch · started by u/peak_area_pete