274
Interferences
The following ions may interfere when present in concentrations
exceeding those listed below.
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.
Substance Concentration and Suggested Treatments
Acidic or basic
samples
Adjust to approximately pH 7. Use 1 N Sodium Hydroxide
Standard Solution for acidic samples and 1 N Hydrochloric Acid
Standard Solution 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.
3. The interference will then be successfully blanked out.
Nitrite 600 mg/L as NO
2
-
-N
Nitrate 5,000 mg/L as NO
3
-
-N
Orthophosphate 5,000 mg/L as PO
4
3-
-P
Sulfate 6,000 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. Swirl to mix.
3. Filter the sample through folded filter paper. Use the filtered
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.
NITROGEN, AMMONIA, High Range, Test 'N Tube, continued
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