57-30
NITRITE, HR, continued
SAMPLING AND STORAGE
Collect samples in clean plastic or glass bottles.
The following storage instructions are necessary only when prompt
analysis is not possible. 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, add 4.0 mL of Mercuric
Chloride Solution for each liter of sample taken and mix. Sample
refrigeration is still required. Do not use acid preservatives.
ACCURACY CHECK
Standard Solution Method
Dissolve 0.150 grams of fresh sodium nitrite and dilute to 1000 mL with
demineralized water to prepare a 100 mg/L nitrite standard solution.
Prepare this solution daily.
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 79.8 mg/L NO
2
-
concentration samples, the standard deviation was ±3.8 mg/L NO
2
-
.
Testing zero concentration samples, the limit of detection was 3.9 mg/L
NO
2
-
. 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
This test does not measure nitrates nor is it applicable to glycol based
samples. Dilute glycol based samples and follow the Nitrite, Low
Range Procedure (DR/700 Filter Module 50.01).
SUMMARY OF METHOD
The method uses ferrous sulfate in an acidic medium to reduce nitrite to
nitrous oxide. Ferrous ions combine with the nitrous oxide to form a
greenish-brown complex in direct proportion to the nitrite present.
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