Hach DR/850, Procedures Manual, Page: 230 / 460

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4. Dilute to volume with organic-free water, cap and mix
thoroughly. This is a 2.00 mg/L buffered ammonia standard.
5. Pipet 50.0 mL of the buffered ammonia standard into a clean
100-mL beaker. Add a stir bar.
6. Obtain a recent lot of Chlorine Solution Ampules,
50–70 mg/L, and note the actual free chlorine concentration
for this lot.
7. Calculate the amount of Chlorine Solution to be added to the
ammonia standard using the following equation:
8. Open an ampule and, using a glass Mohr pipet, add the
calculated amount of Chlorine Solution slowly to the
ammonia standard, while mixing at medium speed on a stir
plate.
9. Allow the monochloramine solution to mix for 1 minute after
all Chlorine Solution is added.
Important Note: Because of
the strong buffer used in the
preparation of this standard,
it cannot be used for accuracy
verification of the Free
Ammonia test.
10. Quantitatively transfer the monochloramine solution to a
clean 100-mL Class A volumetric flask. Dilute to the mark
with organic-free water, cap, and mix thoroughly. This is a
nominal 4.5 mg/L (as Cl
2
) monochloramine standard.
Use this standard within 1 hour of preparation.
Accuracy Check (Free Ammonia Test, Program 46)
Dilution water is required when testing a diluted sample and
preparing standard solutions. Dilution water must be free of
ammonia, chlorine and chlorine demand. A convenient source is
a recirculating, deionizer system with carbon filtration which
produces 18 megaohm-cm water.
Standard Additions Method
1.
Measure 50 mL of sample into three 50-mL mixing cylinders.
2. Use the TenSette Pipet to add 0.3, 0.6, and 1.0 mL of
Ammonium Nitrogen Standard, 10 mg/L as NH
3
-N to the
three samples. Mix well.
mL chlorine solution required
455
free chlorine concentration
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Nitrogen, Free Ammonia and Chloramine (Mono), continued