LaMotte 1200 Colorimeter User Manual
Page 71
NOTE: For the best possible results, carry a reagent blank through the procedure. After
scanning the blank in Step 4, perform the test procedure on clear, colorless, distilled or
deioized water. Subtract results of regent blank from all subsequent test results.
NOTE: If the reading displays
Er2
, repeat procedure on diluted sample, and multiply
the result by the appropriate dilution factor. See 1200 Colorimeter Instruction Manual
for procedure.
CALCULATIONS
To express results as Unionized Ammonia (NH
3
):
Unionized Ammonia (NH
3
) = ppm Ammonia Nitrogen (NH
3
-N) x 1.2
To express results as Ionized Ammonia (NH
4
+
):
Ionized Ammonia (NH
4
+
) = ppm Ammonia Nitrogen (NH
3
-N) x 1.3
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
4
-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 find 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 ppm 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
FW
1
SW
2
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
14.97
12.40
1
Freshwater data from Trussel (1972).
2
Seawater values from Bower and Bidwell (1978). Salinity for the Seawater values =
34% at an ionic strength of 0.701 m.
3