Hach DR/700 Procedures Manual page 282

NITRATE, HR,
continued
ACCURACY CHECK
Standard Additions Method
a) Snap the neck off a fresh High Range Nitrate Nitrogen Voluette
-
Ampule Standard, 500 mg/L NO -N.
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b) Use the TenSette Pipet to add 0.1, 0.2, and 0.3 mL of standard to three
25-mL samples. Mix each thoroughly. (For AccuVac ampuls, use 25 mL
in 50-mL beakers.)
c) Analyze each sample as described above. The nitrogen concentration
should increase 2.0 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
Use a 10.0 mg/L Nitrate Nitrogen Standard Solution listed under
Optional reagents to check test accuracy. Or, this can be prepared by
diluting 1.00 mL of solution from a High Range Nitrate Nitrogen
-
Voluette Ampule Standard Solution, 500 mg/L NO -N, to 50.0 mL with
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demineralized water.
PRECISION
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 30.0 mg/L NO -N
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concentration samples, the standard deviation was ±3.40 mg/L NO
-
-N.
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Testing zero concentration samples, the limit of detection was 0.66 mg/L
-
NO -N. The limit of detection was calculated as three times the
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standard deviation when testing zero concentration samples (Adapted
from Analytical Chemistry, 1980, 52, 2242-2249)
Using one representative lot of AccuVacs, the standard deviation was
±2.70 mg/L NO
- -
-N and the limit of detection was 0.64 mg/L NO -N.
3 3
INTERFERENCES
This method registers both the nitrate and nitrite nitrogen present in the
sample. If nitrite is present, the nitrite nitrogen test using program
number 50.08.1 should be performed on the sample. The amount of
nitrite nitrogen found should be subtracted from the results of the nitrate
nitrogen test when the following pretreatment is used:
50-32