The determination of nitrate and nitrite concentration is one of the most frequent needs in environmental investigations. Numerous analytical methods exist and the reduction of nitrate to nitrite for quantitative colorimetry has proven to be both sensitive and very reliable for flow injection analysis. A copperized cadmium column is used to catalyze the reduction of nitrates into nitrites in a reproducible and quantitative fashion. Nitrites will react with sulfanilamide to form azo dyes that will then couple with N-(1-Naphthyl) ethylenediamine dihydrochloride to form magenta colored solution. This azo dye solution can be quantified at 540 nm and is proportionate to the quantity of nitrate present.