Hach DR/700 Procedures Manual page 603

NITROGEN, AMMONIA,
continued
b) Add the contents of one Sulfide Inhibitor Reagent Powder Pillow.
Swirl to mix.
c) Filter the sample through a folded filter paper.
d) Use the filtered solution in Step 4.
Iron interferes with the test. Eliminate iron interference as follows:
a) Determine the amount of iron present in the sample following one of
the Total Iron procedures.
b) Add the same iron concentration to the demineralized water sample in
Step 5.
The interference from iron in the sample will then be successfully
blanked out in Step 11.
Extremely acidic or alkaline samples should be adjusted to approximately
pH 7. Use 1 N Sodium Hydroxide Standard Solution for acidic samples
or 1 N Sulfuric Acid Standard Solution for basic samples.
Less common interferences such as hydrazine and glycine will cause
intensified colors in the prepared sample. Turbidity and sample color will
give high values. Samples with severe interferences require distillation.
Albuminoid nitrogen samples also require distillation. Hach recommends
the distillation procedure using the Hach General Purpose Distillation Set.
See Optional Apparatus listing. The distillation procedure is detailed in the
Nitrogen, Ammonia - Nessler Method.
SUMMARY OF METHOD
Ammonia compounds combine with chlorine to form monochloramine.
Monochloramine reacts with salicylate to form 5-aminosalicylate. The
5-aminosalicylate is oxidized in the presence of a sodium nitroprusside
catalyst to form a blue-colored compound. The blue color is masked by
the yellow color from the excess reagent present to give a final green-
colored solution.
61-47