Hach DR/850 Procedures Manual page 281

NITROGEN, TOTAL INORGANIC, Test 'N Tube,
Interferences
Summary of Method
In a single laboratory, using a standard solution of 20.0 mg/L
-
NO N and 2 representative lots of reagent with the instrument, a
2
single operator obtained a mean recovery of 14.6 mg/L with a
standard deviation of
± 0.77 mg/L N (replicate number = 7 per reagent lot).
Estimated Detection Limit
The estimated detection limit for program 68 is 0.7 mg/L N. For
more information on the estimated detection limit, see Section 1.
The following ions may interfere when present in concentrations
exceeding those listed below:
Species
Calcium
Manganese (IV)
Magnesium
Sulfide
Sulfate
The following do not interfere below the levels listed:
Species
3+
Al
2+
Ba
2+
Cu
3+
Fe
2+
Zn
-
F
3-
PO -P
4
SiO
2
EDTA
Titanium (III) ions reduce nitrate and nitrite to ammonia in a
basic environment. After centrifugation to remove solids, the
ammonia is combined 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.
281
continued
Level
1000 mg/L as CaCO
3
3 mg/L
1000 mg/L as CaCO
3
3 mg/L
250 mg/L
Level
8 mg/L
40 mg/L
40 mg/L
8 mg/L
80 mg/L
40 mg/L
8 mg/L
80 mg/L
80 mg/L
Effect
Positive
Negative
Positive
Negative
Negative