Filter Wheel Setting (Fld-3400Rs Only) - Thermo Scientific Dionex UltiMate 3000 Series Operating Instructions Manual

5.7.3 Filter Wheel Setting (FLD-3400RS only)

To prevent this stray light from reaching the PMT, additional optical edge filters are
installed in the light path between the flow cell and the emission monochromator. This
reduces direct scattering of light from the light source. In addition, a grating
monochromator lets unwanted fractions (the half, one third, ...) of a selected wavelengths
pass. If the monochromator is set to 500 nm, for example, second-order stray light at 250
nm from the sample may reach the PMT. The filters also eliminate this higher-order stray
light.
Ideally, these filters let all wavelengths above their cut-off wavelength pass, while light with a
smaller wavelength than the cut-off wavelength is blocked. In practice, there is a transition
area where the transmission of the light increases from the lower wavelengths near the range
where the light is cut off to the higher wavelengths near the range where the light passes.
Fig. 37 shows the transmission behavior of the 280 nm filter, which is the filter that is
installed in the FLD-3100 before the emission monochromator.
The FLD-3400RS provides a filter wheel that is located before the emission monochromator.
The filter wheel carries several optical filters with different cut-off lengths. The qualitative
transmission behavior of all filters is shown in Fig. 37, with a transmission range of approx.
+/- 30 nm. At the cut-off wavelength, the filters let 50% of the light pass. The filter wheel
setting can be selected automatically or manually.
If the filter wheel mode is set to Auto, the detector automatically selects a filter wheel
•
position. It selects the first filter with a cut-off wavelength below the selected emission
wavelength. This mode is selected by default and provides best results for most
applications.
Operating Instructions
Fluorescence Detectors FLD-3100 and FLD-3400RS
Fig. 37: Transmission behavior of the 280 nm filter
UltiMate 3000 Series:
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