G-12 Theory and Principles of Operation
and stitches the values into the spectrum to produce a better representation of
the peak with valid accurate mass.
Rule: You must configure the DRE Magnification Factors before acquiring
data in DRE mode. These factors must also be reconfigured if you change any
of the tuning parameters or ion mode.
See also: Setting up DRE mode on page 4-15.
Tip: When you acquire data in the DRE mode, Waters recommends that you
scan at a rate of at least 5 spectra per second. This gives better peak shapes
and more accurate intensity representation.
Multiple peak stitching
When a very intense ion signal strikes the detector it can affect the
neighboring ion signal from the isotope ions. This is because the baseline
drops leading the to isotope ions being recorded at lower intensities than the
real value.
When using Multiple Peak Stitching the DRE software will check the signal of
the ion in the high intensity data. If it exceeds a level where it will affect its
neighboring isotopes then the isotope peak is also stitched in from the weak
data in addition to the strong main peak. In the weak data the baseline is not
affected and therefore the isotope ratio will be correct.
When stitching in the weak intensity data the software will look in a window
defined by the parameters “Pre Window” – for how many Da before the strong
peak and “Post Window” - for how many Da after.
If you find that the isotope ratios are incorrect for very intense molecules in
DRE experiments then the Multiple Peak Stitching option should be used. For
most organic molecules the default values of 0 Da for Pre Window and 2 Da for
Post Window are suitable. However with some molecules for example a large
chlorinated sample it may be sensible to increase these numbers to catch all
the ion envelope.
However using Multiple Peak Stitching will stitch in all the low intensity data
around the mass of interest. This means that any small co-eluting peak in this
mass range could be missed.
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