Dead time correction B-49
To set up resolution parameter manually:
1. Observe a beam of tris (trifluoromethyl) triazine.
2. Use the reference reservoir pump valve to reduce the amount of
reference sample until there are less than 1000 ion counts per second in
continuum mode to avoid saturation effects.
3. Acquire data in continuum mode and sum up several spectra so there
are more than 2000 ion counts peak height viewed in the spectrum.
4. Measure full-width-half-maximum (FWHM) resolution of the peak at
m/z 285.
5. Use the following equation to calculate the resolution:
Tip: Resolution should be greater than 7000, (when measured at the
614 peak of heptacosa) Resolution reduces as the peak mass reduces.
6. In the MassLynx Tune window, click .
7. In the TDC Settings dialog box, type the calculated resolution value in
the Resolution field.
Note: Resolution is automatically determined by the Instrument Setup
wizard.
See also: Instrument Setup Wizard Introduction: on page 3-9.
Dead time correction
The data acquisition system for the instrument is a time-to-digital (TDC)
converter, an ion counting system that generates a mass spectrum by creating
a histogram of ion arrival times of ions in memory. After the arrival and
registration of an ion by the TDC, a minimum time interval occurs before a
subsequent ion arrival can be registered. The interval is called the dead time
of the TDC and is of the order of 5 ns. If more than one ion arrives in the same
time increment, then only one count is registered.
At high ion currents, some of the ion arrivals are not registered, this leads to a
shift to lower mass centroids and lower measured areas on reported peaks.
Resolution
Mass
FWHM
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