61-45
NITROGEN, AMMONIA, continued
13. Press: READ
The display will
count down to 0.
Then the display will
show the results in
mg/L NH
3
as N.
Note: To convert results
to other units, see
Table 1.
SAMPLING AND STORAGE
Collect samples in clean plastic or glass bottles. Most reliable results
are obtained when samples are analyzed as soon as possible after
collection.
If chlorine is known to be present, the sample must be treated
immediately with sodium thiosulfate. Add one drop of 0.1 N Sodium
Thiosulfate Standard Solution for each 0.3 mg of chlorine present in a
one liter sample.
To preserve samples, adjust the pH to 2 or less with concentrated
sulfuric acid (about 2 mL per liter). Store samples at 4 °C or less.
Samples preserved in this manner can be stored up to 28 days. Just
before testing the stored sample, warm to room temperature and
neutralize with 5.0 N Sodium Hydroxide Standard Solution. Correct the
test result for volume additions; see Sampling and Storage, Volume
Additions, (Section I) for more detailed information.
ACCURACY CHECK
Standard Additions Method
a) Measure 25 mL of sample into three 25-mL mixing cylinders.
b) Use the TenSette Pipet to add 0.2, 0.4, and 0.6 mL of Nitrogen
Ammonia Standard, 10 mg/L as NH
3
-N to the three samples. Mix well.
Table 1. Conversion Factors
To convert reading from To Multiply by
mg/L NH
3
-N mg/L NH
4
+
1.29
mg/L NH
3
-N mg/L NH
3
1.22
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