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Aquaprobe
®
AP-5000 Instruction Manual
10401-00906 Rev M
15.5. 2000/5000-BGA-PC Freshwater Blue-Green Algae (phycocyanin) Electrode
Freshwater Blue-Green Algae (BGA-PC) can be measured by the AP-5000 using the
optional 2000/5000-BGA-PC optical electrode.
15.5.1.
Principle of Operation
The 2000/5000-BGA-PC optical electrode is a submersible, fixed response fluorometer,
which provides excitation at 590nm and detects any resultant fluorescence above 655nm.
The electrode induces the phycocyanin to fluoresce, then measures the longer wavelength
light which is emitted as a result of the fluorescence process.
15.5.2.
Limitations of Use
Determination of BGA-PC 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 phycocyanin 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 BGA.
•
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
.
15.5.3.
Calibrating the BGA-PC Electrode
The BGA-PC electrode has two calibration points. Careful calibration is essential in order to
ensure consistent and reliable results.
When a BGA-PC 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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