Hach DR2400 - Page 477

Nitrogen, Ammonia
Nitrogen, Ammonia
NitrogenAmm_TNT_High_SAL_Eng_Ody.fm Page 3 of 6
Interferences
In some lab environments, airborne cross contamination of the blank is possible.
Complete preparation of the blank before opening or handling any samples or
standards to avoid transfer of ammonia. If sample or standard containers have
already been open, move to a separate area of the lab to prepare the blank.
Sample Collection, Storage, and Preservation
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 (Cat. No. 323-32) 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 at least 2 mL of
Hydrochloric Acid (Cat. No. 134-49). Store at 4 °C (39 °F) or less. Preserved
samples may be stored up to 28 days. Warm samples to room temperature.
Neutralize to a pH of 7.0 with 5.0 N Sodium Hydroxide (Cat. No. 2450-26) before
analysis. Correct the test result for volume additions.
Interfering Substance Interference Levels and Treatments
Acidic or basic samples
Adjust to approximately pH 7. Use 1 N Sodium Hydroxide Standard Solution (Cat. No. 1045-32)
for acidic samples and 1 N Hydrochloric Acid Standard Solution (Cat. No. 134-49) for basic
samples.
Calcium 50,000 mg/L as CaCO
3
Glycine, hydrazine Will cause intensified colors in the prepared sample.
Magnesium 300,000 mg/L as CaCO
3
Iron
Eliminate iron interference as follows:
1. Determine the amount of iron present in the sample using 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.
Nitrite 600 mg/L as NO
2
–
–N
Nitrate 5000 mg/L as NO
3
–
–N
Orthophos-phate 5000 mg/L as PO
4
3–
–P
Sulfate 6000 mg/L as SO
4
2–
Sulfide
Sulfide will intensify the color. Eliminate sulfide interference as follows:
1. Measure about 350 mL of sample in a 500-mL Erlenmeyer flask.
2. Add the contents of one Sulfide Inhibitor Reagent Powder Pillow (Cat. No. 2418-99).
Swirl to mix.
Filter the sample through folded filter paper (Cat. No. 692-57). Use the solution in step 4.
Turbidity and color
Give erroneous high values. Samples with severe interferences require distillation.
Hach recommends the distillation procedure using the Hach General Purpose Distillation Set
(Cat. No. 22653-00).