85
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 HI7609829‑10 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.
APPENDIX C - ISE INFORMATION
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