Aquaprobe
®
AP-700, AP-800 & AP-2000 Instruction Manual
10401-00870 Rev R
16.8. 2000/5000-RHOD Rhodamine WT Electrode
Rhodamine WT is a fluorescent red dye that is commonly used in water flow studies and
can be measured by the Aquaprobe
®
using the optional 2000/5000-RHOD optical
electrode.
16.8.1.
Principle of Operation
The 2000/5000-RHOD optical electrode is a submersible, fixed response fluorometer,
which provides excitation at 520nm and detects any resultant fluorescence above 575nm.
The electrode induces the Rhodamine to fluoresce, then measures the longer wavelength
light which is emitted as a result of the fluorescence process.
16.8.2.
Limitations of Use
Measurement of Rhodamine in the field using fluorescence measurement techniques can
be adversely affected by:
•
Interference from microbiological species and compounds, which fluoresce at similar
wavelengths.
•
Differences in the fluorescent response caused by temperature.
•
Differences in the fluorescent response caused by ambient light.
•
Interference caused by turbidity.
The normal affects of temperature on the fluorescent response of Rhodamine is
automatically compensated for by the electrode.
16.8.3.
Calibrating the RHOD Electrode
The RHOD electrode has two calibration points. Careful calibration is essential in order to
ensure consistent and reliable results.
When a RHOD 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.
16.8.4.
Calibration Solution Preparation
In order to 'calibrate' the RHOD electrode, a 100µg/L calibration solution of Rhodamine WT
should be used. This is exactly the same calibration solution that is recommended for
calibration of the BGA-PC electrode.
The 100µg/L calibration solution should be freshly prepared by serial dilution from 200g/L
standard using deionised water. The following Rhodamine WT standard is recommended:
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