Hach DR/700 Procedures Manual page 614

NITROGEN, MONOCHLORAMINE,
Manual. Standard 1 (S1) is made by pouring 10 mL of sample into a
zeroing vial or 10-mL sample cell. Cap the cell. Edit the display to
show 00.00 mg/L. For standard 2 (S2), edit the display to show 00.55
mg/L and 1.124 Abs.
INTERFERENCES
Ammonia contamination from air is a common cause of high results.
Ampules, beakers and other containers may require rinsing with excess
sample just before use. Samples, solutions, and demineralized water
will accumulate ammonia from the air.
The following ions may interfere when present in concentrations
exceeding those listed below:
Calcium
Magnesium
pH
Sulfate
This method is not recommended for the determination of ammonia in
non-chlorinated samples that have a chlorine demand greater than 2
mg/L as Cl .
2
Mixtures of small amounts of differing substances may interfere. To
assess the influence of these interferences in a sample, perform the
Accuracy Check, Standard Addition Method.
SUMMARY OF METHOD
This method determines "free ammonia" in the presence of
monochloramine. Monochloramine (NH
+
and NH ) can exist in drinking water sample where chloramine
4
disinfection is used. Hypochlorite is added to combine with free
ammonia to form additional monochloramine. Monochloramine reacts
with salicylate to form 5-aminosalicylate in the presence of a
cyanoferrate catalyst to give a green solution. Free ammonia is
determined by measuring the color intensities, with and without added
hypochlorite.
3000 mg/L as CaCO
1600 mg/L as CaCO
less than 7
> 900 mg/L as SO
Cl) and free ammonia (NH
2
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continued
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