Nitrite is a naturally occurring inorganic form of nitrogen. It is relatively unstable as it is the intermediate species between ammonia and nitrate. Hence, it is usually found in very low concentrations in the environment, less than 0.1 mg/L, and its concentration does not normally exceed 1 mg/L in municipal wastewater.
WHY IS IT IMPORTANT?
Nitrite is the intermediate oxidation state of nitrogen in the oxidation of ammonia to nitrate, and in the reduction of nitrate. Therefore, although it is generally a short-lived compound it provides important information on the kinetics of nitrification and denitrification processes. Due to its high toxicity, a limit of 1 mg/L has been imposed on drinking water.
The most common method for nitrite measurement is Method 353.3. Samples are run through a cadmium column to reduce nitrate to nitrite. Nitrites react with an added reagent and generate a red coloured solution whose absorbance is then measured spectrophotometrically at 543 nm. The absorbance of the solution is directly proportional to the concentration of nitrite in the sample. Additionally, nitrite nitrogen can be measured by ion chromatography, and flow injection analysis.