Sensitivity (Detector Sensitivity) - Thermo Scientific Dionex UltiMate 3000 Series Operating Instructions Manual

5.7.2 Sensitivity (Detector Sensitivity)

The sensitivity is used to optimize the signal-to-noise ratio in a chromatogram. Depending
on the intensity of the fluorescence, it may be necessary to adjust the sensitivity several
times during an analysis. To find the best sensitivity, it is required to determine the
maximum emission intensities. This section describes a method for this and the technical
background.
Background
A PMT (or optionally two PMTs) measures the intensity of the emission light after the
emission monochromator. The sensitivity of the PMT can be adjusted in 8 steps (1 to 8) with
the Sensitivity parameter. With each step, the sensitivity of the PMTs increases by
approximately a factor 2. If a peak with sensitivity = 5 is 15 million counts high, for example,
the peak height increases to 30 million counts when the sensitivity = 6 (→ Fig. 35).
• If the selected sensitivity is too small, the peak height is reduced and the signal-to-noise
ratio is not optimal (→ Fig. 35, Sensitivity = 1).
If the selected sensitivity is too large, the PMT signal is saturated. In this case, the
•
detector automatically reduces the sensitivity. Lines appear in the chromatogram at the
beginning and at the end of the saturation (→ Fig. 35, Sensitivity = 8). If the detector is
not saturated any more, the Sensitivity setting before saturation is restored.
Tips: When the sensitivity was automatically reduced or when the initial value was
restored, the Chromeleon Audit Trail shows a warning with the new sensitivity
value after the adjustment.
Calibration depends on the PMT. Therefore, calibration and quantification
must always be performed with the same PMT.
Operating Instructions
Fluorescence Detectors FLD-3100 and FLD-3400RS
UltiMate 3000 Series:
Page 81