89
HI 7609829-12: Nitrate ion selective electrode is a combination liquid mem-
brane sensor used for the detection of nitrate nitrogen in freshwater samples.
The sensor utilizes a polymeric membrane made with nitrate ionophore in a PVC
head and a silver/silver chloride double junction gel filled reference electrode.
The outer body of the sensor is the thermoplastic PEI. This sensor is used in place
of the pH sensor in the probe.
The measurement of Nitrate-Nitrogen, NO
3
-
-N is a useful tool in the measurement
of surface water contaminants such as tracing the source of agricultural
operations runoff or studying nutrient levels in natural waters. HI 7609829-12
is an ion selective sensor that responds to the free nitrate ion.
Although all forms of nitrogen including nitrogen gas (N
2
) are interconvertible
within the nitrogen cycle as a function of oxidation state, the nitrate sensor only
detects the ionized form.
HI 7609829-12 is specified for 0.62 to 200 ppm (mg/L) NO
3
-
-N (equivalent
to 2.74 - 885.6 ppm (mg/L) NO
3
-
). Based on the corresponding molecular
weights of nitrogen and nitrate, the relationship is: NO
3
-
-N =(NO
3
-
)(14/
62)=(NO
3
-
) x
0.2258.
The sensor responds in a Nernstian manner (like a pH sensor) and produces a
voltage that the meter converts to a concentration value.
HI 7609829-12 Nitrate ion sensor linearity@ 25°C
100
150
200
250
300
350
0.1 1 10 100 1000
log ppm NO
3
-
-N
mV
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