66 1100 Series FD Reference Manual
3 Optimizing the Fluorescence Detector
Finding the Best Signal Amplification
Increasing the PMTGAIN increases the signal and the noise. Up to a certain
factor the increase in signal is higher than the increase in noise.
The step from gain to gain is equal to a factor of 2 (which is the same as on the
HP 1046A FLD).
In Figure 27 the PMTGAIN was gradually raised from 4 up to 11 (the peak is
from the Agilent Technologies isocratic sample which was diluted 1000
times). With increasing PMTGAIN there was an improvement in signal-to-noise
up to 10. Above 10 the noise increased proportionately to the signal with no
improvement in signal-to-noise.
The reason for this is the fact, that quantification of baselines (especially at
low background levels) is not sufficient for statistically working filter
methods. For the best gain, check your solvent under flow conditions with the
auto-gain function. Do not use higher values than proposed by the system, if
not necessary, because of excessive high fluorescence signals.
Use the PMT test to automatically determine the setting.
Figure 27 Finding Best PMTGAIN for Biphenyl
6
8
9
4
PMT
10
11
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