998-2300 Rev. H Page 28
Appendix D: Linear Range, Quenching and Temperature Considerations
The linear range is the concentration range in which the C3 sensor output is directly
proportional to the concentration of the signal. The linear range begins with the
smallest detectable concentration and spans to an upper limit (concentration) that is
dependent upon the properties of the material, filters used, and path length.
A non-linear relationship is seen at very high concentrations where the signal does
not increase at a constant rate in comparison to the change in concentration (see
figure below). At even higher concentrations, the signal will decrease even though
the sample concentrations are continuing to increase. This effect is known as
“signal quenching”.
Linearity can be checked by diluting a sample 1:1 or some other convenient ratio. If
the sample is still in the linear range, the reading will decrease in direct proportion to
the dilution. If the reading does not decrease in direct proportion to the dilution or if
the reading increases, the sample is beyond the linear range.
Temperature Considerations
Fluorescence is temperature sensitive. As the temperature of the sample increases,
the fluorescence decreases. For greatest accuracy, record the sample temperature
and correct the sensor output for changes in temperature.
For further information on how temperature, light, water quality and the physiological
state of the algal cells can all affect the measurement of chlorophyll a, please refer
to the application section of Turner Designs’ website.
Graph showing Linear and
Quenching Regions of the
sample’s response
Sample Concentration
Fluorometer
Fluorometer Response Curve
Sample
Quenching Region
Sample
Linear Region
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