[Lab] CPC cagri — Janoshik came back 98.1% against a claimed 97.5%
CPC cagri — Janoshik came back 98.1% against a claimed 97.5%. One vial, one service, one member paying, which is the only kind of result this board should treat as evidence.
98.1% and 97.5% — those are the numbers, and they are the ones I am willing to defend.
Retention time shifted 0.4 minutes and I assumed the worst. It was the column temperature.
Bought a second-hand instrument and learned more in six months of fixing it than in three years of reading traces.
Sceptical readings welcome. The confident ones are the ones I distrust.
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nofollow and sponsored; nobody here is paid for it.best — the order this archive was captured in
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.
What did system suitability look like on that sequence?
Disagree. Inter-lab spread of a point or two on this assay is ordinary and calling it a discrepancy misleads people.
baseline choice is a decision, not a measurement
Gave the same trace to two people I trust and got two integrations about a point apart. That was the most educational afternoon I have had here.
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.
Started reporting my own integrations with the baseline choice stated. Arguments in my threads dropped by about half.
integration decisions move the number more than the sample does
Yes — system suitability first. Without it the number is an assertion about the instrument, not the sample.
Right. And a blank between injections settles the carryover argument before it starts.
How old is the column and roughly how many injections has it seen?
What wavelength, and what was the gradient?
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.
- 1Resolution between two peaks depends on retention, selectivity and…7 comments in this branch · started by u/samir_falk