Aquaprobe
®
AP-700, AP-800 & AP-2000 Instruction Manual
10401-00870 Rev R
16.7. 2000/5000-CPHYLL Chlorophyll Electrode
Chlorophyll can be measured by the Aquaprobe
®
using the optional 2000/5000-CPHYLL
optical electrode.
16.7.1.
Principle of Operation
The 2000/5000-CPHYLL optical electrode is a submersible, fixed response fluorometer,
which provides excitation at 470nm and detects any resultant fluorescence above 630nm.
The electrode induces the chlorophyll to fluoresce, then measures the longer wavelength
light which is emitted as a result of the fluorescence process.
16.7.2.
Limitations of Use
Determination of chlorophyll in the field using fluorescence measurement techniques will
never be as accurate as measurements made in a lab using either cell counting or analysis
of molecular chlorophyll after its extraction from cells.
Factors adversely affecting accuracy include:
•
Interference from other microbiological species and compounds, which fluoresce at
similar wavelengths.
•
Differences in the fluorescent response between various species of phytoplankton.
•
Differences in the fluorescent response caused by temperature.
•
Differences in the fluorescent response caused by ambient light.
•
Interference caused by turbidity.
Fluorescence measurement techniques are ideal for researchers who are interested in
detecting the presence or absence of a specific substance and measuring relative
fluorescence changes that can be used as an indication of increasing or decreasing
concentrations.
Fluorescence measurement techniques are not ideal for quantitative measurement. In
order to obtain more accurate results, data obtained with the fluorometer in the field should
be post-calibrated with data from standard laboratory analysis of grab samples acquired
during the study.
If grab sample data is available, a Grab Sample Factor (GS Factor) should be calculated
and input on the calibration screen in order to improve the accuracy of future readings.
16.7.3.
Calibrating the CPHYLL Electrode
The CPHYLL electrode has two calibration points. Careful calibration is essential in order to
ensure consistent and reliable results.
When a CPHYLL electrode is first installed,
it MUST be calibrated at both points
in order
to set the electrode's relative sensitivity and establish its slope.
Subsequently, a single point (Zero) calibration should be carried out daily. Full two-point
calibration should be carried out every few months.
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®
Ltd.
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