Hach DR/850, Руководство по процедурам, Страница: 267 / 460

267
c) Analyze each sample as described above. The nitrogen
concentration should increase 0.20 mg/L for each 0.1 mL
of standard added.
d) If these increases do not occur, see Standard Additions ,
Section 1 , for more information.
Standard Solution Method
To check accuracy, use a 1.0 mg/L Nitrogen, Ammonia Standard
Solution listed under Optional Reagents. Or, dilute 1 mL of
solution from a
50 mg/L Ampule Standard for Nitrogen, Ammonia to 50 mL with
deionized water using a 50-mL volumetric flask.
Method Performance
Precision
In a single laboratory, using a standard solution of 1.0 mg/L
ammonia nitrogen and two representative lots of reagent with the
instrument, a single operator obtained a standard deviation of
+0.02 mg/L NH
3
-N.
Estimated Detection Limit
The estimated detection limit for program 66 is 0.08 mg/L NH
3
-
N. For more information on the estimated detection limit, see
Section 1 .
Interferences
Interfering Substance Interference Level and Treatment
Calcium 2500 mg/L as CaCO
3
Iron 1. Determine the amount of iron present in the sample following one of the total
iron procedures.
2. Add the same iron concentration to the deionized water in step 4. The
interference will then be successfully blanked out.
Magnesium 5000 mg/L as CaCO
3
Nitrite 30 mg/L as NO
2
-
-N
Nitrate 250 mg/L as NO
3
-
-N
Orthophosphate 250 mg/L as PO
4
3-
-P
pH Acidic or basic samples should be adjusted to about pH 7. Use 1 N Sodium
Hydroxide Standard Solution for acidic samples and 1 N Hydrochloric Acid
Standard Solution for basic samples.
Sulfate 300 mg/L as SO
4
2-
NITROGEN, AMMONIA, Low Range, Test 'N Tube,
continued