256
Sampling and Storage
Collect samples in clean plastic or glass bottles.
Store at 4 °C (39 °F) or lower and analyze within 48 hours. Warm
to room temperature before running the test.
Do not use acid preservatives.
Remove suspended solids by filtration.
Accuracy Check
Standard Solution Method
Pipet 5.00 mL of a fresh Hach standard, 250 mg/L as NO
2
-
-N into
a Class A 250-mL volumetric flask. Dilute to the line with
deionized water to make a 5.00-mg/L intermediate standard.
Pipet 10.00 mL of the 5.0-mg/L intermediate standard into a
Class A 500-mL volumetric flask. Dilute to the line with
deionized water to make a 0.100 mg/L NO
2
-
-N standard solution.
Prepare immediately before use.
Run the test using the 0.100 mg/L NO
2
-
-N standard in place of the
sample. Results should be between 0.090 and 0.110 mg/L NO
2
-
-N.
9.
Cover the sample cell
tightly with the
instrument cap.
10. Press: ZERO
The cursor will move to
the right, then the
display will show:
0.000 mg/L NO2-N
Note: If the reagent blank
correction is on, the display
may flash “limit.” See
Section 1.
11. Place the prepared
sample in the adapter.
Push straight down on
the top of the vial until it
seats solidly into the
adapter.
Note: Do not move the vial
from side to side as this can
cause errors.
12. Tightly cover the
sample cell with the
instrument cap.
Press:
READ
The cursor will move to
the right, then the result
in mg/L nitrite nitrogen
(or an alternate form)
will be displayed.
Note: Standard Adjust may
be performed using a
prepared standard
(see Section 1).
NITRITE, Test 'N Tube, continued
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