Biology Reference
In-Depth Information
4
Notes
1. When multiple SRM transitions for a given substance are cho-
sen, the individual signal intensities are added to a single sig-
nal. This should also be considered when comparing high mass
accuracy and resolution FullScan methods with SRM/MRM
methods as well as the generation of the mass spectrometer,
instrument parameters, and complexity of the underlying sam-
ple matrix.
2. False positive signals can be disregarded and do not necessarily
distort quantifi cation, since true signals can reliably be identi-
fi ed by comparing the retention time, peak shape, and relative
transition order of a HP-LP-pair.
3. Since metabolites most frequently are detected with a single
charge, the precursor is larger than its product
m
/
z
value, and
SRM transitions whose precursor is smaller than its product
m
/
z
value can't be selected.
4. The systematic shift of Peak Area values (arbitrary units),
between the two instruments does not imply any qualitative or
quantitative difference.
5. Reducing the scan range (Full Scan or Selected Ion Monitoring)
elevates the signal to noise ratio and improves sensitivity, how-
ever, useful information may thus become unavailable [
15
].
Elevating target Automatic Gain Control (AGC) values can
improve the dynamic range, due to elevated sensitivity for low
concentrations, but can lead to negative space charge effects at
high concentrations [
12
].
Acknowledgments
We thank Thomas Naegele for useful comments and discussions.
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