Hach-Lange NISE sc - Manual (Page 9)

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General information
Figure 3 Sensor cartridge
2.3 Functional principle
Ion-selective electrodes have a special membrane to which only a specific type of ion can
adhere. As a result, an ion-specific potential forms on the membrane surface. To measure
a potential difference, a reference system is required that will not be affected by the
sample to be measured.
The CARTRICAL TM technology reduces cross-sensitivity by calibrating not only the
individual electrodes but also the measuring electrode against the compensation
electrode and the reference; this is carried out at the factory. The reference system is
designed using pH-differential technology and is therefore particularly stable in terms of
drift and contamination.
2.3.1 AN-ISE sc probe
The AN-ISE sc probe uses the ion-selective electrode technology to measure ammonium
ions (NH
4
+ ) and nitrate ions (NO
3
– ) in a waste water sample.
Known interfering factors due to potassium (when measuring ammonium), chloride (when
measuring nitrate) and temperature are compensated by suitable built-in electrodes.
1 Ammonium electrode 1,2
1 Active with AN-ISE sc
2 Active with AISE sc
5 Reference system
2 Nitrate electrode 1,3
3 Active with NISE sc
6 Temperature sensor
3 Potassium electrode 1,2 7 Marker hole for assembling the probe
4 Chloride electrode 1,3