The amperometric H2 micro-sensor has been developed
for the insitu determination of hydrogen containing aqueous solutions.
Therefore the sensor is suitable for direct measurements in coloured and
turbid solutions and in sediments. Special applications of the sensor
are the measurement in deep sea volcanic ares, measurements in the
condensate of compost factories and in power stations,
but also in the chemical industry to follow chemical reactions.
Compared with all the other commercially available hydrogen sensors this
amperometric hydrogen microsensor works with such a 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 H2 sensors is
the very fast response time of the AMT hydrogen microsensor with t90%
below 2 seconds compared with a minimum of approximately 30 to 120
seconds in the case of the conventional sensors.
The third advantage of the new microsensor is based on the micro-sensor
technology. The signal stability of amperometric hydrogen microsensors
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 the gaseous H2 dissolved in the
sample, the analyte is separated from the inner electrolyte by the
membrane. The membrane is only pervious to gases, so that liquids, ions
and solids are not able to reach the inner electrolyte or the electrodes
of the sensor. The sensor contains inside a special electrolyte and 3
The electrode materials have been choosen and prepared very carefully to
realize ideal electrochemical conditions.
The time for the polarization, realized by means of the sensors
integrated electronic device, is approximately 15 to 30 minutes after
the first switching or long breaks. If the hydrogen has passed now the
membrane, it is transported by diffusion to the working electrode
followed by the electrochemically oxidation of the H2. This causes a
current depending on the hydrogen partial pressure/hydrogen
concentration of the sample. The observed current within a range of 0...400
picoamperes is converted into a voltage of 0...5 Volt inside the
integrated electronic device of the sensor. Besides, in opposite to
other measuring principles, the current flow in the amperometric sensor
leads to a rapid decrease of the analyte inside the sensor resulting in
very fast response times even though there is a concentration jump from
high to low concentrations.
All electrochemically working sensors have to be combined with a
temperature measurement and the amperometric hydrogen 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
have 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.
The advantages of the micro-sensor technology
For manufacturing the amperometric H2 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 for the hydrogen to the working electrode and a
negligible analyte consumption at the electrodes leading finally to
response times (t90%) of less than 2 seconds. The analyte consumption
effects are negligible too, so that streaming of the sensor 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 sediments
Technical data for all H2-micro-sensor heads
independent from the sensordesign *)
measuring principle: amperometric membrane
3 sensor electrodes
exchangeable sensor head
necessary time for the first polarization:
approx. 15-30 minutes
streaming of the membrane or stirring is not
necessary, low analyte consumption
suitable for the determination of concentration
gradients with high local resolution
measuring ranges: 0,0002....3 mg/l H2 others on
accuracy of the sensor:: better than 2% of the
temperature range: 0°C to 30°C
response times: t90%: below 2 seconds
average life time: approximately 6-10 months,
may be influenced by the samples matrix
pressure stability: laboratory sensor or shallow
water version for pressures of up to 10 bar or
housing: all housings made of titanium
Sensor designs of amperometric H2
1.) Laboratory microsensor with integrated electronic
This sensor has been developed for
the 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 hydrogen 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
The shallow water sensor has been developed for use
in combination with so called CTD-probe systems up to depths of 70
meters. 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
hydrogen 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