Sensors
©
2021
– Valeport Ltd
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2.4.1.4 Rhodamine WT
Performance
Excitation:
520 nm
Detection:
650 nm
Dynamic Range:
0 - 1000 ppb
Instrument Detection limit: <0.01 ppb*
Actual Detection limit:
0.06 ppb**
Linearity:
0.99 R
2
Response Time:
0.03 to 2 s
* 3x SD in RO water
** Calibrated against Rhodamine solution
2.4.1.5 Linear Observation Range
The linear range is the concentration range for which the fluorometer signal is directly proportional
to the concentration of the fluorophore. The linear range starts at the minimum detection limit
(MDL) and extends to the upper limit of the instrument (dependent on fluorophore properties,
optical filters, LED power, sample volume and optical path length).
Valeport Fluorometers have a calibrated linear response for 2 gain settings (e.g. the ranges 0-40
µg/l (G5) and 0-800 µg/l (G1) for chlorophyll a). At higher concentrations, unlike analogue devices
which generally flat-line at full-scale deflection (e.g. FSD 5V) the fluorometer will continue to
output a signal which increases with concentration (i.e. meaningful data), though which is no
longer guaranteed to be linear.
At very high fluorophore concentrations, signal quenching can occur, whereby the instrument
output does not increase linearly with fluorophore concentration (roll-off) and may decrease at
even higher levels.
To perform a quick linearity check, dilute the sample 1:1 with RO water. If the reading decreases
by 50%, the sample is in the linear range. If the reading decreases by less than 50% or even
increases, the sample is above the linear range.
