APPENDIX
Ammonia in water occurs in two forms: toxic unionized ammonia (NH
3
) and the relatively
non-toxic ionized form, ammonium ion (NH
4+
). This test method measures both forms as
ammonia-nitrogen (NH
3
–N) to give the total ammonia-nitrogen concentration in water.
The actual proportion of each compound depends on temperature, salinity, and pH. A
greater concentration of unionized ammonia is present when the pH value and salinity
increase.
1. Consult the table below to fi nd the percentage that corresponds to the temperature,
pH, and salinity of the sample.
2. To express the test result as ppm Unionized Ammonia-Nitrogen (NH
3
–N), multiply the
total ammonia-nitrogen test result by the percentage from the table.
3. To express the test result as Ionized Ammonia-Nitrogen (NH
4+
–N), subtract the
unionized ammonia-nitrogen determined in Step 2 from the total ammonia-
nitrogen.
10°C
15°C
20°C
25°C
pH
FW1
SW2
FW
SW
FW
SW
FW
SW
7.0
0.19
----
0.27
----
0.40
----
0.55
----
7.1
0.23
----
0.34
----
0.50
----
0.70
----
7.2
0.29
----
0.43
----
0.63
----
0.88
----
7.3
0.37
----
0.54
----
0.79
----
1.10
----
7.4
0.47
----
0.68
----
0.99
----
1.38
----
7.5
0.59
0.459
0.85
0.665
1.24
0.963
1.73
1.39
7.6
0.74
0.577
1.07
0.836
1.56
1.21
2.17
1.75
7.7
0.92
0.726
1.35
1.05
1.96
1.52
2.72
2.19
7.8
1.16
0.912
1.69
1.32
2.45
1.90
3.39
2.74
7.9
1.46
1.15
2.12
1.66
3.06
2.39
4.24
3.43
8.0
1.83
1.44
2.65
2.07
3.83
2.98
5.28
4.28
8.1
2.29
1.80
3.32
2.60
4.77
3.73
6.55
5.32
8.2
2.86
2.26
4.14
3.25
5.94
4.65
8.11
6.61
8.3
3.58
2.83
5.16
4.06
7.36
5.78
10.00
8.18
8.4
4.46
3.54
6.41
5.05
9.09
7.17
12.27
10.10
8.5
5.55
4.41
7.98
6.28
11.18
8.87
14.96
12.40
1
Freshwater data from Trussel (1972).
2
Seawater values from Bower and Bidwell (1978). Salinity for Seawater values = 34% at an
ionic strength of 0.701m.
SMART Spectro 2 Test Procedures 07.05.16
APPENDIX
Appendix
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