YSI 9300 Photometer - Manual (Page 81)

PHOTOMETER TEST INSTRUCTIONS
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Nitrates are normally present in natural, drinking and waste waters. Nitrates
enter water supplies from the breakdown of natural vegetation, the use of
chemical fertilisers in modern agriculture and from the oxidation of nitrogen
compounds in sewage effluents and industrial wastes.
Nitrate is an important control test for water supplies. Drinking waters
containing excessive amounts of nitrates can cause methaemoglobinaemia in
bottle-fed infants (blue babies). The EEC has set a recommended maximum of
5.7 mg/l N (25 mg/l NO
3
) and an absolute maximum of 11.3 mg/l N (50 mg/l
NO
3
) for nitrate in drinking water.
The YSI Nitratest method provides a simple test for nitrate nitrogen over the
range 0 - 1 mg/l N. The test can however be extended to cover the range 0 - 20
mg/l by a simple dilution technique.
Method
In the YSI Nitratest method nitrate is first reduced to nitrite, the resulting nitrite
is then determined by a diazonium reaction to form a reddish dye.
The reduction stage is carried out using the unique zinc-based Nitratest Powder,
and Nitratest Tablet which aids rapid flocculation after the one minute contact
period. The test is conducted in a special Nitratest Tube - a graduated sample
container with hopper bottom to facilitate settlement and decanting of the sample.
The nitrite resulting from the reduction stage, is determined by reaction with
sulphanilic acid in the presence of N-(1-naphthyl)-ethy!ene diamine to form a
reddish dye. The reagents are provided in a single Nitricol tablet which is simply
added to the test solution.
The intensity of the color produced in the test is proportional to the nitrate con-
centration and is measured using a YSI Photometer.
Photometer Method
AUTOMATIC
WAVELENGTH
SELECTION
0 – 1 mg/l N
0 – 20 mg/l N
PHOT.23.AUTO