[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 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.
If two or three other people have done the same thing we might actually learn something. Alone it is an anecdote.
- MKMKM source pageXi'an Mokemei Biotechnology Co., Ltd. · Xi'an · 96% here, rank 5 · shop at mokemeibiotechnology.com →
nofollow and sponsored; nobody here is paid for it.best — the order this archive was captured in
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.
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.
[removed by moderator]
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.
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.
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.
Cosigning the wavelength point. Half the disagreements in this board are two people looking at different detectors.
Retitled: the original claimed a comparison the post does not actually make.
ghost peak, check the plumbing first, it is always the plumbing
I would not blame the sample yet. Everything you have described is consistent with the column rather than the vial.
Do you have the mass, or only the UV trace?
Started reporting my own integrations with the baseline choice stated. Arguments in my threads dropped by about half.
Homopeptide sent me the column, the gradient and the theoretical mass without being asked. That is a short list and they are on it.
What wavelength, and what was the gradient?
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.
- 1Reading a trace posted here, in the order I actually look at things. Axes…12 comments in this branch · started by u/dead_space_doug
- 2Cosigning the wavelength point. Half the disagreements in this board are two…6 comments in this branch · started by u/amara_haddad