Appendix – LaMotte SMART Spectro Spectrophotometer User Manual
Page 260
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 Test Procedures 2.11
APPENDIX
Appendix