30 Agilent InfinityLab LC Series 1260 Infinity II FLD User Manual
1
Introduction to the Fluorescence Detector
Analytical Information From Primary Data
You can amplify the signal using PMTGAIN. Depending on the PMTGAIN you
have set, a multiple of electrons is generated for every photon falling on the
photomultiplier. You can quantify large and small peaks in the same
chromatogram by adding PMTGAIN changes during the run into a timetable.
Figure 16 PMTGAIN: Amplification of Signal
Check proposed PMTGAIN. Deviations of more than 2 PMT gains should be
corrected in the method.
Each PMTGAIN step is increased approximately by a factor of 2 (range 0 - 18).
To optimize your amplification for the peak with the highest emission, raise
the PMTGAIN setting until the best signal-to-noise is achieved.
After the photons are converted and multiplied into an electronic signal, the
signal (at present analog) is tracked and held beyond the photo-multiplier.
After being held, the signal is converted by an A-to-D converter to give one raw
data point (digital). Eleven of these data points are bunched together as the
first step of data processing. Bunching improves your signal-to-noise ratio.
The bunched data, shown as larger black dots in Figure 17 on page 31, is then
filtered using a boxcar filter. The data is smoothed, without being reduced, by
taking the mean of a number of points. The mean of the same points minus the
first plus the next, and so on, is calculated so that there are the same number
of bunched and filtered points as the original bunched points. You can define
the length of the boxcar element using the RESPONSETIME function: the
longer the RESPONSETIME, the greater the number of data points averaged. A
four-fold increase in RESPONSETIME (for example, 1 sec to 4 sec) doubles the
signal-to-noise ratio.
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