Micromass Quattro Ultima, User Manual

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Ion Counting Threshold
Ion Counting Threshold
sets the intensity level below which a data point is
ignored. This threshold is applied to all acquisitions, regardless of scanning mode. It is
also the most significant of all of the data manipulation variables as it is applied to the
raw data first.
When an acquisition is started the instrument performs a ‘prescan’ with the ion beam
switched off so that the electronic noise level of the acquisition system and its
standard deviation can be measured.
The Ion Counting Threshold level entered is multiplied by the standard deviation
of the noise to determine the intensity level to be used.
•
Values can be set between 0 and 1000, the higher the number the more data is
discarded.
•
If a value of zero is entered the intensity level is set so that it sits in the middle
of the noise which means that roughly half of the noise data is acquired.
•
A value of 10 places the threshold just above the noise so almost all of the data
is acquired.
•
If a value of 60 is entered the threshold sits well above the noise level, so very
little noise data is acquired.
•
A value of 30 is suitable for most data. A value of zero disables the facility.
When using an Ion Counting Threshold other than zero, both Profile Data ,
Baseline Level and SIR Baseline Level should be set to zero.
Ion Counting Threshold
should be set so that background noise is removed
without significantly reducing the intensity of the smallest peaks of interest.
The following table shows the effects of changing baseline noise and ion counting
threshold on background noise and low intensity peaks.
Data Acquisition
Page 77
Quattro Ultima
User's Guide