Hach DR/700 Procedures Manual page 289

NITRATE, LR,
continued
SAMPLING AND STORAGE
Collect samples in clean plastic or glass bottles. Store at 4 °C (39 °F) or
lower if the sample is to be analyzed within 24 to 48 hours. Warm to
room temperature before running the test. For longer storage periods,
adjust sample pH to 2 or less with sulfuric acid, ACS (about 2 mL per
liter). Sample refrigeration is still required.
Before testing the stored sample, warm to room temperature and
neutralize with 5.0 N Sodium Hydroxide Standard Solution. Do not use
mercury compounds as preservatives. Correct the test result for volume
additions; see Sampling and Storage, Volume Additions, (Section I) for
more information.
ACCURACY CHECK
Standard additions Method
a) Measure 30 mL of sample into three cylinders.
b) Using the TenSette Pipet, add 0.1, 0.2, and 0.3 mL of Nitrate
-
Nitrogen, Voluette Ampule Standard Solution, 12 mg/L as (NO -N), to
3
the three samples. Mix well.
c) Analyze each sample as described above. The nitrate nitrogen
concentration should increase 0.04 mg/L for each 0.1 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 nitrate nitrogen standard by diluting 2.00 mL of the
10 mg/L Nitrate Nitrogen Standard Solution to 100 mL with
demineralized water. Or, using the TenSette pipet, make a 0.12 mg/L
nitrate nitrogen standard by diluting 1.0 mL of a Nitrate Nitrogen
Voluette Ampule Standard Solution, 12 mg/L, 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 0.30 mg/L NO N
-
3
concentration samples the standard deviation was ±0.012 mg/L NO
N.
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3
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