Hanna Instruments HI 9829 - Manual (Page 90)

90
The calibration solutions and displayed measurements are as ppm Ammonium-
nitrogen
. Due to the space restriction of the display the unit of measurement
will be displayed as “ppmAm”.....
The ammonium 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 ammonium 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 7609829-10 is selective toward ammonium ions, it also responds
to other ions which can interfere with the measurement. The ratio of interfering
ion to ammonium ion must be less than the ratio indicated below:
Sodium: 90
Potassium: 0.75
Calcium: 125
Magnesium: 4000
Exposure to these interferences does not cause permanent damage to the sensor.
Note that the potassium ion interference is the strongest, and its concentration
must be less than the ammonium concentration to have no effect.
HI 76098290-10 Ammonium ion sensor linearity @25°C
-100
-50
0
50
100
150
0.01 0.1 1 10 100 1000
log ppm NH
4
+ N
mV