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METHODS AND INTERFERENCES
Test Factor
Method
Alkalinity
Buffered indicator reagent
Ammonia
Salicylate
Calcium
Buffered indicator reagent
Hardness
Buffered indicator reagent
Magnesium
Buffered indicator reagent
Nitrate
Zinc reduction, Diazotization
Nitrite
Diazotization
pH
Mixed indicators
Phosphate
Phosphomolybdate, Stannous
chloride/ascorbic acid reduction
CONVERSIONS
Ammonia (NH
) Ammonia in water occurs in two forms: toxic unionized ammonia (NH
3
relatively non-toxic ionized form, ammonium ion (NH
both forms as ammonia (NH
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 find the percentage that corresponds to the temperature, pH, and salinity
of the sample.
2. To express the test result as ppm Unionized Ammonia (NH
result by the percentage from the table.
3. To express the test result as ppm Ionized Ammonia (NH
determined in step 2 from the Total Ammonia.
pH
Fresh
water
1
7.0
0.19
7.1
0.23
7.2
0.29
7.3
0.37
7.4
0.47
7.5
0.59
7.6
0.74
7.7
0.92
7.8
1.16
7.9
1.46
8.0
1.83
8.1
2.29
8.2
2.86
8.3
3.58
8.4
4.46
8.5
5.55
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.
) to give the total ammonia concentration in water. The actual
3
10°C
Salt
Fresh
water
2
water
—
0.27
—
0.34
—
0.43
—
0.54
—
0.68
0.459
0.85
0.577
1.07
0.726
1.35
0.912
1.69
1.15
2.12
1.44
2.65
1.80
3.32
2.26
4.14
2.83
5.16
3.54
6.41
4.41
7.98
Interferences
Alkalinity < 20 ppm, Quats and polyquats in
high concentrations
Nitrite above 5 ppm, High concentrations of
reducing agents
Calcium > 800 ppm, Magnesium > 2000 ppm
None
pH <7, pH >9, Borates > 200 ppm
Chlorine neutralizer containing sodium
thiosulfate
Copper > 10 ppm
Turbidity
Iron > 5 ppm, Ammonia >5 ppm
+
). This test method measures
4
+
4
15°C
Salt
Fresh
water
water
—
0.40
—
0.50
—
0.63
—
0.79
—
0.99
0.665
1.24
0.836
1.56
1.05
1.96
1.32
2.45
1.66
3.06
2.07
3.83
2.60
4.77
3.25
5.94
4.06
7.36
5.05
9.09
6.28
11.18
10
), multiply the Total Ammonia test
3
), subtract the Unionized Ammonia
20°C
Salt
Fresh
water
water
—
0.55
—
0.70
—
0.88
—
1.10
—
1.38
0.963
1.73
1.21
2.17
1.52
2.72
1.90
3.39
2.39
4.24
2.98
5.28
3.73
6.55
4.65
8.11
5.78
10.00
7.17
12.27
8.87
14.97
) and the
3
25°C
Salt
water
—
—
—
—
—
1.39
1.75
2.19
2.74
3.43
4.28
5.32
6.61
8.18
10.10
12.40
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