Hach DR/850, Procedures Manual, Page: 280 / 460

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d) Analyze each sample as described in the procedure; use a
1-mL aliquot of the prepared sample in Step 5. The
nitrogen concentration should increase about 1.8 to 1.9
mg/L for each 0.1 mL of standard added.
e) If these increases do not occur, see Standard Additions in
Section 1 for more information.
Standard Solution Method
To check accuracy, use a 10.0 mg/L Nitrate Nitrogen Standard
Solution listed under Optional Reagents. Alternatively, a 20.0
mg/L nitrate nitrogen standard can be prepared by diluting 2 mL
of solution from a PourRite Ampule Standard for High Range
Nitrate Nitrogen, 500 mg/L NO
3
- -N, to 50 mL with deionized
water. Substitute this standard for the sample and perform the test
as described. The recovery of the standards should be about
90-95%.
Method Performance
Precision/Accuracy
The total inorganic nitrogen test provides an estimate of the total
nitrite, nitrate, and ammonia nitrogen load in water or wastewater
samples. This test is most applicable for monitoring an industrial
process stream or a wastewater treatment stream where it is
important to track the inorganic nitrogen load as it passes through
the treatment process. The test exhibits different recoveries of
each of the three nitrogen species, as summarized below. This test
is not recommended for quantifying only one of the three species.
In that case, use a specific procedure for each particular analyte.
Ammonia Nitrogen
In a single laboratory, using a standard solution of 20.0 mg/L
NH
3
-
N and 2 representative lots of reagent with the instrument, a
single operator obtained a mean recovery of 21.3 mg/L with a
standard deviation of
± 0.77 mg/L N (replicate number = 7 per reagent lot).
Nitrate Nitrogen
In a single laboratory, using a standard solution of 20.0 mg/L
NO
3
-
N and 2 representative lots of reagent with the instrument, a
single operator obtained a mean recovery of 18.9 mg/L with a
standard deviation of
± 0.55 mg/L N (replicate number = 7 per reagent lot).
Nitrite Nitrogen
NITROGEN, TOTAL INORGANIC, Test 'N Tube,
continued