[Question] LC-MS — what am I missing here
LC-MS — what am I missing here — that is what I am asking, and I have already read the wiki twice.
Bought a second-hand instrument and learned more in six months of fixing it than in three years of reading traces.
QYB sent me the column, the gradient and the theoretical mass without being asked. That is a short list and they are on it.
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.
Not medical advice, obviously, and nothing here is approved for human use. One person with a spreadsheet.
best — the order this archive was captured in
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.
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.
That figure cannot be quoted to two decimals off that baseline. The precision is not in the data.
LC-MS for identity, UV for relative quantity
Disagree. Inter-lab spread of a point or two on this assay is ordinary and calling it a discrepancy misleads people.
214nm sees the peptide bond, 280nm sees the aromatics
Started reporting my own integrations with the baseline choice stated. Arguments in my threads dropped by about half.
How old is the column and roughly how many injections has it seen?
Careful — you are treating retention time as identity. Two things can co-elute and the trace will not tell you.
This. A shoulder that does not baseline-resolve is a question, not a quantity.
Ran a blank after a high-concentration injection and found the carryover I had been calling an impurity.
Push back: a longer run is not automatically better resolution. You are trading peak width for time and the ratio is what matters.
Is that baseline drawn by the software or by hand?
What wavelength, and what was the gradient?
report the method or do not report the number
system suitability before you believe any number on the run
- 1This. A shoulder that does not baseline-resolve is a question, not a quantity.7 comments in this branch · started by u/ewan_marchand