[Lab] MKM cagri — Medutest came back 97.7% against a claimed 97.0%
Right: MKM cagri — Medutest came back 97.7% against a claimed 97.0%. I paid for this one myself, nobody sent me anything, and the receipts are in the comments. The relevant figures are 97.7% and 97.0%, and they come from the same log I have kept the whole time. Retention time shifted 0.4 minutes and I assumed the…
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.
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system suitability before you believe any number on the run
Did you run a blank between injections?
Did you run a blank between injections?
This is the whole methodological point of the board in one line.
Chased a ghost peak for three weeks. It was the plumbing. It is always the plumbing.
Careful — you are treating retention time as identity. Two things can co-elute and the trace will not tell you.
Right. And a blank between injections settles the carryover argument before it starts.
integration decisions move the number more than the sample does
What did system suitability look like on that sequence?
Is that baseline drawn by the software or by hand?
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.