Hach DR/850, Procedures Manual, Page: 257 / 460

257
Method Performance
Precision
In a single laboratory, using a standard solution of 0.250 mg/L
nitrite nitrogen and two representative lots of reagent with the
instrument, a single operator obtained a standard deviation of
±0.004 mg/L NO
2
- -N.
Estimated Detection Limit
The estimated detection limit for program 63 is 0.006 mg/L NO
2
-
-N. For more information on derivation and use of Hach’s
estimated detection limit, see
Section 1 .
Interferences
Summary of Method
Nitrite in the sample reacts with sulfanilic acid to form an
intermediate diazonium salt. This couples with chromotropic acid
to produce a pink-colored complex directly proportional to the
amount of nitrite present.
Interfering
Substance
Interference Levels
Antiminous ions Interfere by causing precipitation
Auric ions Interfere by causing precipitation
Bismuth ions Interfere by causing precipitation
Chloroplatinate ions Interfere by causing precipitation
Cupric ions Cause low results
Ferric ions Interfere by causing precipitation
Ferrous ions Cause low results
Lead ions Interfere by causing precipitation
Mercurous ions Interfere by causing precipitation
Metavanadate ions Interfere by causing precipitation
Nitrate Very high levels of nitrate (>100 mg/L nitrate as N) appear to
undergo a slight amount of reduction to nitrite, either spontane-
ously or during the course of the test. A small amount of nitrite
will be found at these levels.
Silver ions Interfere by causing precipitation
Strong oxidizing and
reducing
substances Interfere at all levels
NITRITE, Test 'N Tube,
continued