Hanna Instruments HI 9829 Instruction Manual page 90

The calibration solutions and displayed measurements are as ppm Nitrate-
nitrogen. Due to the space restriction of the display the unit of measurement
will be displayed as "ppmNi".
The nitrate sensor will last longer in colder clean waters than in severely
contaminated water or warmer waters. This is because the active chemicals
responsible for the nitrate ion sensitivity are leached out of the membrane with
continued exposure. As the sensor ages there will be a decreased sensitivity until
the sensor will no longer calibrate or operate properly. The lifetime of the sensor
depends greatly on deployment conditions.
Although HI 7609829-12 is selective toward nitrate ions, it also responds to
other ions which can interfere with the measurement. Organic solvents and
cationic detergents must be absent. Chloride has the largest interference for
natural waters.
The ratio of interfering ion to nitrate ion must be less than the ratio indicated
bel o w:
Fluoride: 300
Chloride:100
Carbonate: 4
Nitrite: 4
Iodide: 0.01
Perchlorate: 0.0045
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