purity — 19 things I got wrong before I got it right
purity — 19 things I got wrong before I got it right, which sounds obvious until you try to state the evidence for it.
Area percent is the integrated area of your peak over the total integrated area at one wavelength on one gradient. Change any of those and the number changes without the sample changing.
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.
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.
Screenshot none of this. Read the whole thread, including the parts where I am told I am wrong.
best — the order this archive was captured in
Retitled: the original claimed a comparison the post does not actually make.
That figure cannot be quoted to two decimals off that baseline. The precision is not in the data.
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.
system suitability before you believe any number on the run
Bought a second-hand instrument and learned more in six months of fixing it than in three years of reading traces.
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.
Careful — you are treating retention time as identity. Two things can co-elute and the trace will not tell you.
Careful — you are treating retention time as identity.
This is the whole methodological point of the board in one line.
Mass spectrometry answers identity. UV purity answers relative quantity under the run conditions. A document with one and not the other is answering half the question, and the half it answers should be stated.
report the method or do not report the number
Correction: that is a tailing factor, not a plate count. Different diagnostics for different problems.
Retention time shifted 0.4 minutes and I assumed the worst. It was the column temperature.
axis labels or the trace is decoration
That is area percent, not mass percent. The trace cannot give you the second one.
Correcting myself upthread: I said the gradient was linear and looking again it has a hold in the middle.
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