Nitrate in effluent samples is
determined by injecting the sample
into an imidazole buffer stream
(pH 7.5). This stream carries the
sample over a copperized cadmium
reactor which reduces the nitrate to
nitrite. This stream is merged with a
coloring reagent comprising
sulfanilamide and NED. A violet
color, which is monitored photometrically
at 555 nm, results.