Geoscience Reference
In-Depth Information
Light - before it enters the
sample cuvette
(excitation monochromator)
Light
source
Slit
Mirror
Sample cuvette
Detector
Light as it leaves the
sample cuvette
(emission monochromator)
Figure 5.7. A typical spectrofluorimeter configuration.
5.3.2 Basic Spectrofluorimeter Design
Many spectrofluorimeter systems have a typical configuration similar to that presented
in
Figure 5.7
. Illumination sources are typically steady-state xenon arc discharge lamps,
coupled to scanning monochromators to make a tunable light source. The sample is illu-
minated at a certain wavelength,
λ
exc
, and the resulting luminescence measured using a
second monochromator to select an emission wavelength,
λ
em
, and detected usually with a
photomultiplier detector.
5.4 Measuring Fluorescence
5.4.1 Defining the Sensing Volume and Inner Filter Effects
All fluorescence measurements require that the instrument should provide a source of pho-
tons. These photons are generated by a light source, selected for an excitation wavelength,
λ
exc
, by the excitation monochromator, which also selects a specific pass-band of wave-
lengths
Δλ
exc
. For aquatic samples a geometrically defined volume of sample, usually in
a cuvette, will be illuminated via an excitation source. During illumination light from a
