General informations about the amperometric ozone micro-sensor
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Amperometric Ozone micro-sensor
Determination of dissolved ozone in aqueous solutions
The amperometric O3 micro-sensor has been developed for the insitu determination of ozone
containing aqueous solutions. Therefore the sensor is suitable for direct measurements in coloured,
turbid and solid containing solutions. Compared with all the other commercially available ozone
sensors this amperometric ozone micro-sensor contains a redox catalyst and works with a very low
analyte consumption, that streaming of the sensor membrane or stirring of the analyte is not
necessary. And, an additional stirrer is not necessary for stationary measurements. The second
advantage of the micro-sensor compared to other ozone sensors is the very fast response time of the
AMT ozone micro-sensor with t90% below 4,5 seconds compared with a minimum of approximately
80 to 120 seconds in the case of the conventional sensors. The third advantage of the new microsensor is based on the micro-sensor technology itself. The signal stability of amperometric ozone
micro-sensors is essential better. And the high local signal resolution allows some new applications,
as for instance the profiling in µm-steps. Besides, measurements in soft sediments or muds became
also practicable.
The general working principle of the sensor
Because of the partial pressure of gaseous ozone dissolved in the sample, the analyte is separated by
permeation through the membrane. The membrane is only pervious for gases, so that liquids, ions
and solids are not able to reach the inner electrolyte of the sensor. The sensor contains inside an
electrolyte with a redox catalyst (= redox mediator) and 3 electrodes. The electrode materials have
been choosen and prepared very carefully to realize ideal electrochemical conditions. At the
electrodes a special polarization voltage is adjusted to realize a well-defined concentration ratio of
the oxidized and of the reduced form of the redox catalyst. The time for the polarization, realized by
means of the sensors integrated electronic device is approximately 5-10 minutes. If the ozone passes
now the membrane, it reacts first chemically with the redox catalyst to form a reaction product
followed by the electrochemically reduction of the reaction product at the working electrode. Caused
by the polarization voltage the system is now endeavoured to adjust the former concentration ratio.
This causes a current similar to the dissolved ozone amount of the sample. Besides, the current flow
in the amperometric sensor leads to a rapid decrease of the analyte inside the sensor resulting in very
fast response times also, if a rapid change from high to very low concentration levels is necessary.
All electrochemically working sensors have to be combined with a temperature measurement and
the amperometric ozone sensor too. When ordering a multisensor measuring system for laboratory
use or a complete submersible probe system, the temperature measurement and the temperature
correction of the sensor signal is already included. If measurements in a flow through system are
required, special temperature sensors for the integration in AMT flow through cells are offered.
When measuring in opened vessels or beakers in the laboratory, the customers has to realize the
temperature measurement themselves. If a calibrated sensor is ordered, the temperature correction is
very easy by means of a factor or for more accurate measurements by means of a mathematical
formula, delivered with the sensor.
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AMT Analysenmesstechnik GmbH
2001
General informations about the amperometric ozone micro-sensor
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The advantages of the micro-sensor technology
For manufacturing the amperometric O3 sensor, a special geometric design has been choosen to built
a real micro-sensor. Electrode diameters below 25 µm, a very thin special membrane with small
diameters, extremly short diffusion distances to the working electrode and a negligible analyte
consumption at the electrodes leading finally to response times (t90%) of less than 5 seconds. The
analyte consumption effects are negligible too, so that streaming of the sensors membrane and
stirring is not necessary. Besides, the dimensions of the sensitive tips within a range of some
micrometers allow insitu measurements without destroying equilibriums, concentration gradients
and geometrical structures. This is very important, if measurements in muddy solutions are required.
Technical Data for all O3-micro-sensor heads independent from the sensordesign *)
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measuring principle: amperometric membrane covered microsensor with redox catalyst
3 sensor electrodes
exchangeable sensor head
measuring range:
20 µg/l...10 mg/l O3 (linear range)
others on request
accuracy of the sensor:: better than 2% of the measuring value
resolution: > 2 µg/l per digit
response times:
t90%: below 4,5 seconds
t90%: below 9 seconds
(If the sensor is used the first time or after long breaks, a short 2 minutes long activation with
a ozone concentration of approximately 0,5 mg/l is necessary.)
pressure stability:
laboratory sensor or
shallow water version for pressures of up to 10 bar
average life time: approximately 5-10 months, may be influenced by the samples matrix
housing: all housings made of titanium
polarization: necessary, switching on is realized automatically with sensor switching on
necessary time for polarization: 5-10 minutes
residual current: approx. 1-5 pA, temperature independent,
changes not within the sensors life
temperature range: -2°C to 30°C
signal interferences: not against oxygen and chlorine, but signal interferences against H2O2 if
the concentration is more than 2 Vol.%
streaming of the membrane or stirring is not necessary, low analyte consumption
suitable for the determination of concentration gradients with high local resolution
*) Changes for technical improvement are reserved.
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AMT Analysenmesstechnik GmbH
2001
General informations about the amperometric ozone micro-sensor
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Sensor designs of amperometric ozone micro-sensors
1.) Laboratory microsensor with integrated electronic device
This sensor has been developed for laboratory and simple field use and has to be combined with one
of the offered measuring devices. The sensor consists of a titanium housing, a waterproof connection
with the cable (IP 68), an exchangeable sensor head and a removable protection cage (on your own
risk - no guarantee in the case of mechanical destruction). This sensor could be equipped both with
the ozone sensor head and with a galvanic oxygen sensor head. Other concentration ranges can be
delivered on request. The exchange of the sensor head is very easy by pull off and push on. Please
take note, that no liquid can get in to the plug connection when changing the sensor head.
2.) Shallow water microsensor for probe systems
The shallow water sensor has been developed for use in combination with so called CTD-probe
systems up to depths of 100 meters and for applications with up to 10 bar pressure. Therefore every
shallow water sensor is equipped with a special underwater connector, type wet con BH-4-MP.
Further characteristics are the integrated electronic device, the titanium housing and the
exchangeable sensor head. This sensor could be equipped both with the ozone sensor head and with
a galvanic oxygen sensor head. Other concentration ranges can be delivered on request. The
exchange of the sensor head is very easy by pull off and push on. Please take note, that no liquid can
get in to the plug connection when changing the sensor head.
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AMT Analysenmesstechnik GmbH
2001
General informations about the amperometric ozone micro-sensor
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Use of amperometric ozone micro-sensors
1. Laboratory use:
2. Field measurements
(up to 1 m water depth):
3. Online insitu measurements
(up to 100 meter water depth)
laboratory sensor with integrated electronic device
+ simple or multisensor measuring device with cable
+ temperature sensor
a) laboratory sensor with integrated electronic device
+ simple or multisensor measuring device with cable
+ temperature sensor or
b) submersible probe with sensors for O3 (shallow water version), temperature, pressure (depth)
+ cable
+ notebook/personal computer
+ software
a) submersible probe with sensors for O3 (shallow water
version), pressure (depth), temperature
+ cable
+ notebook/personal computer
+ software
b) Interfacing of already existing probe systems with a
O3 shallow water sensor, provided that the probe system contains one more free channel and is equipped
already with sensors for temperature and pressure
+ integration of the mathematical formula for the
calculation of the hydrogen concentration into the
probe's software
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AMT Analysenmesstechnik GmbH
2001