34 Agilent 6400 Series Triple Quad LC/MS Concepts Guide
2 Inner Workings – Triple Quadrupole MS versus Single Quadrupole MS
How Triggered Dynamic MRM works
that is not marked as a Primary transition but that has the
same compound name as a Primary transition is a secondary
transition for the compound.
You specify a threshold for each Trigger MRM. If the abundances
for the Trigger MRM transitions are greater than the specified
thresholds and the other triggering conditions are met, then the
secondary transitions are acquired. If you have two Trigger
MRM transitions for a compound, then the abundances for both
of these transitions must be greater than or equal to their
thresholds for the secondary transitions to be acquired.
These secondary transitions are acquired for the Number of
Repeats specified. If the trigger transition drops below the
threshold, and rises again above the threshold within the peak
retention time window, the secondary ions are triggered again.
If the retention time window ends, the software stops acquiring
these secondary transitions even if they have not been acquired
for the Number of Repeats specified. The software also stops
acquiring the Primary MRMs when the peak retention time
window ends.
Triggers may happen at different time/abundance
Examination of the abundance of the primary transition(s) and
the decision to sample the additional secondary transitions
happens in real time, on a cycle-to-cycle basis, using unfiltered
data. However, in general, the data stored to disk is the result of
using time filtering (data for a given cycle is smoothed using
data from cycles before and after the given cycle). Therefore,
because of this difference, triggering may appear to start a cycle
or two late, or may appear to trigger at an abundance
significantly different from the trigger threshold set in the
program. Usually, this is not a concern as long as triggering
occurs somewhere during peak elution.
The sample matrix may also affect where triggering occurs. If
triggering is set using a standard made in solvent, the triggering
thresholds may be set to low abundance values. If a sample is
run in matrix where there's a significant response at the trigger
transition due to the matrix, triggering will happen
prematurely. It is preferable to use matrix-matched standards
for calibration and update of the triggering parameters.
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