61-46
NITROGEN, AMMONIA, continued
c) Analyze each sample as described above. The ammonia nitrogen
concentration should increase 0.08 mg/L for each 0.2 mL of standard
added.
d) If these increases do not occur, see Standard Additions (Section I) for
more information.
Standard Solution Method
Prepare a 0.20 mg/L ammonia nitrogen standard by diluting 2.00 mL of
the Nitrogen Ammonia Standard Solution (as NH
3
-N), 10 mg/L, to 100
mL with demineralized water. Or, using the TenSette Pipet, prepare a
0.20 mg/L ammonia nitrogen standard by diluting 0.4 mL of a Ammonia
Nitrogen Voluette Standard Solution, 50 mg/L as NH
3
-N, to 100 mL
with demineralized water.
STATISTICAL EVALUATION
A single operator repetitively tested samples of two laboratory prepared
solutions, using one DR/700, matched sample cells and two representative
lots of testing reagents, Testing 0.400 mg/L NH
3
as N concentration
samples, the standard deviation was ±0.006 mg/L NH
3
as N.
Testing zero concentration samples, the limit of detection was
0.029 mg/L NH
3
as N. The limit of detection was calculated as three
times the standard deviation when testing zero concentration samples
(Adapted from Analytical Chemistry,1980, 52, 2242-2249).
INTERFERENCES
The following ions may interfere when present in concentrations
exceeding those listed below:
Calcium 1000 mg/L as CaCO
3
Magnesium 6000 mg/L as CaCO
3
Nitrite 12 mg/L as NO
2
-
-N
Nitrate 100 mg/L as NO
3
-
-N
Orthophosphate 100 mg/L as PO
4
3-
-P
Sulfate 300 mg/L as SO
4
2-
Sulfide will intensify the color. Eliminate sulfide interference as
follows:
a) Measure about 350 mL of sample in a 500-mL erlenmeyer flask.
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