Hach DR/850, Руководство по процедурам, Страница: 279 / 460

279
Sampling And Storage
Collect samples in clean plastic or glass bottles. Best results are
obtained with immediate analysis.
If chlorine is known to be present, add 1 drop of 0.1 N sodium
thiosulfate for each 0.3 mg/L Cl
2
in a 1 liter sample.
Preserve the sample by reducing the pH to 2 or less with
concentrated hydrochloric acid (at least 2 mL). Store at 4
°
C (39
°
F)
or less. Preserved samples may be stored up to 28 days. Warm
samples to room temperature and neutralize with 5 N Sodium
Hydroxide before analysis. Correct the test result for volume
additions; see
Correcting for Volume Additions in Section 1 .
Accuracy Check
Standard Additions Method
a) Fill three 25-mL graduated mixing cylinders with 25 mL of
sample.
b) Snap the neck off a fresh High Range Nitrate Nitrogen
PourRite Ampule Standard, 500 mg/L NO
3
- -N.
c) Use the TenSette Pipet to add 0.1, 0.2, and 0.3 mL of
standard, respectively, to 3 25-mL mixing cylinders. Mix
thoroughly.
17.
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.
18.
Tightly cover the
sample cell with the
instrument cap.
19.
Press:
READ
The cursor will move to
the right, then the result
in mg/L total inorganic
nitrogen will be
displayed.
Note: Standard Adjust may
be performed using a
prepared standard (see
Section 1).
NITROGEN, TOTAL INORGANIC, Test 'N Tube,
continued