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The sensor responds in a Nernstian manner (like a pH sensor) and produces a voltage that the meter
converts to a concentration value.
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 HI7609829‑12 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 below:
Fluoride: 300 Nitrite: 4
Chloride:100 Iodide: 0.01
Carbonate: 4 Perchlorate: 0.0045
APPENDIX C - ISE INFORMATION
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