Hach DR/850 - Page 281

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In a single laboratory, using a standard solution of 20.0 mg/L
NO
2
-
N and 2 representative lots of reagent with the instrument, a
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.
Interferences
The following ions may interfere when present in concentrations
exceeding those listed below:
The following do not interfere below the levels listed:
Summary of Method
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.
Species Level Effect
Calcium 1000 mg/L as CaCO
3
Positive
Manganese (IV) 3 mg/L Negative
Magnesium 1000 mg/L as CaCO
3
Positive
Sulfide 3 mg/L Negative
Sulfate 250 mg/L Negative
Species Level
Al
3+
8 mg/L
Ba
2+
40 mg/L
Cu
2+
40 mg/L
Fe
3+
8 mg/L
Zn
2+
80 mg/L
F
-
40 mg/L
PO
4
3-
-P 8 mg/L
SiO
2
80 mg/L
EDTA 80 mg/L
NITROGEN, TOTAL INORGANIC, Test 'N Tube, continued