For nitrate determination, 600 mg of zinc powder and
4 mL cadmium sulfate solution were added to 25-mL
volumetric flasks to obtain a homogeneous mixture. After
standing for 10 min, 5 mL of the filtered solution sample
and 5 mL of ammonium buffer were added to the flash. The
solution was stirred for 10 min and then filtered (using
Whatman 41 filter paper) and transferred to a 50-mL
volumetric flask, to which 2.5 mL of the sulfanilamide
reagent was added with mixing. After standing for 5 min at
room temperature, 2.5 mL of the NED reagent was added,
with mixing and dilution to volume. After 15 min, the
absorbance was measured at 540 nm. The nitrate concentration
was calculated as the difference between the total
nitrite concentration after reduction and the initial nitrite
concentration.
Method Validation