ThermoFisher Scientific Vanquish VC-D50, Operating Manual

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3 • Device Overview
Fluorescence Detectors (VC-D50, VC-D51, VF-D50, VF-D51)
Operating Manual Page 33
3.2 Operating Principle
Fluorescence detectors are optical detectors. In a fluorescence detector,
the sample is exposed to light at a defined wavelength. The light is
absorbed by the sample substance and causes the substance to be
placed in an excited state (excitation). As the sample substance returns
to its ground state, it emits light at a higher wavelength (emission). The
photomultiplier tube (PMT) is positioned at an angle of 90° to the light
source and detects the light that was emitted from the fluorescing
substances.
In contrast to UV/VIS detectors, a fluorescence detector measures a very
weak light signal rather than the difference between light intensities
(absorbance).
Absorption of light
Figure 1: Simplified presentation of a molecule absorbing light
Emission of
light of a longer
wavelength
Figure 2: Simplified presentation of a molecule emitting light
(fluorescence)