13
CONVERSIONS
Ammonia (NH
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 (NH
3
) to give the total ammonia 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 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 (NH
3
), multiply the Total
Ammonia test result by the percentage from the table.
3.
To express the test result as ppm Ionized Ammonia (NH
4
+
), subtract the Unionized
Ammonia determined in step 2 from the Total Ammonia.
10°C
15°C
20°C
25°C
pH
Fresh
water
1
Salt
water
2
Fresh
water
Salt
water
Fresh
water
Salt
water
Fresh
water
Salt
water
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 & Bidwell (1978). Salinity for Seawater values = 34% at an ionic strength
of 0.701 m.
