Geoscience Reference
In-Depth Information
Sample
Quenching Region
Sample
Linear Region
Sample Concentration
Figure 6.11. Conceptual diagram showing instrument response and saturation of fluorescence signal
for a highly colored environment.
decrease in fluorescence intensity resulting from the reabsorption of emitted light within a
solution. Previous studies have shown a 20% reduction in fluorescence response above 100
QSE (Gardner et al.,
2005
). To correct for this effect, the fluorescence of sample water and
a series of diluted samples mixed with purified water were measured. A quadratic response
curve (fluorescence vs. % whole water) was then calculated, where the linear portion of the
fitted equation represented instrument response in the absence of the IFE. The correction
factor was determined by dividing the linear portion of the fitted equation by the full equa-
tion, then applying it to the voltage output of the fluorometer. This estimated the response
of the instrument in the absence of inner filtering.
6.4.5 Dynamic Range
Calibration curves are performed to identify the resolution limit, linear range of detec-
tion and saturation range of an instrument (
Figure 6.11
). Therefore dynamic range con-
siderations are imperative when collecting fluorescence measurements. Many sensors are
equipped with adjustable gain settings to maximize the linear range, and analysts can ensure
that measurements do not approach saturation range by serially diluting hand-picked sam-
ples and quantifying any inner filter effects. This is critical for determining whether a sen-
sor is appropriate for a specific application and is discussed further in
Section 6.5
.
6.5 Environmental Considerations
When deploying field sensors, analysts must be aware of environmental factors that can
potentially influence fluorescence measurements. Attributes of a given environment can
be used to decide the ideal optical and sampling designs to yield high-quality fluorescence
