[Method] the gradient everyone uses for sema and why it under-resolves the des-amido
the gradient everyone uses for sema and why it under-resolves the des-amido. It comes up every few weeks and the answer has not changed. 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…
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.
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.
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.
A shoulder that does not baseline-resolve cannot be quantified honestly.
Agreed. And the corollary is that the method line on a certificate is not decoration, it is the number’s provenance.
ghost peak, check the plumbing first, it is always the plumbing
Small fix — 214nm, not 210. It matters for the comparison you are making with the other run.
Agreed.
Adding one practical thing — run the blank. It answers this before anyone has to argue about it.
you cannot report to two decimals off that baseline
retention time alone is not identity
That is area percent, not mass percent. The trace cannot give you the second one.