Hach POCKET COLORIMETER II Instruction Manual page 29

Ammonia, Nitrogen,
• Iron interferes with the test. Eliminate iron interference as follows:
a. Determine the amount of iron in the sample using a total iron analysis.
b. Add the same amount of iron to the deionized water used in the procedure
for the blank. The interference from iron is successfully blanked.
Extremely acidic or alkaline samples should be adjusted to approximately pH 7.
Use 1.0 N Sodium Hydroxide Standard Solution for acidic samples or 1.0 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 erroneous 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
page 1—31.
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