Hach DR/850, Руководство по процедурам, Страница: 273 / 460

273
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 one drop of 0.1 N sodium thiosulfate for each 0.3
mg/L Cl
2
in a one liter sample. Preserve the sample by reducing
the pH to 2 or less with hydrochloric acid (at least 2 mL). Store at
4 °C (39 °F) or less. Preserved samples may be stored up to 28
days. Before analysis, warm samples to room temperature and
neutralize with 5.0 N sodium hydroxide. Correct the test result for
volume additions.
Accuracy Check
Standard Additions Method
a) Snap the top off an Ammonia PourRite Ampule Standard,
150 mg/L NH
3
-N.
b) Use the TenSette Pipet to add 0.2, 0.4 and 0.6 mL of
standard to three 25-mL samples. Swirl to mix.
c) Analyze each sample as described above. The ammonia
concentration should increase approximately 1.2 mg/L
NH
3
-N for each 0.2 mL of standard added.
d) If these increases do not occur, see Standard Additions in
Section 1 for more information.
Standard Solution Method
To check accuracy, use a 10 or 50 mg/L Nitrogen, Ammonia
Standard Solution or use a Nitrogen, Ammonia Voluette Ampule
Standard, 50 mg/L.
Method Performance
Precision
In a single laboratory, using a standard solution of 50 mg/L ammonia
nitrogen (NH
3
-N) and two representative lots of reagent with the
instrument, a single operator obtained a standard deviation of +5 mg/
L NH
3
-N.
Estimated Detection Limit
The estimated detection limit for program 67 is 1 mg/L NH
3
-N.
For more information on the estimated detection limit, see
Section 1 .
NITROGEN, AMMONIA, High Range, Test 'N Tube,
continued