While nitrogen in the form of ammonia, nitrite and nitrate is an essential nutrient for plants and animals, excess nitrogen can be detrimental in many cases.
At Hach®, find the testing equipment, resources, training and software you need to successfully monitor and manage nitrogen levels in your specific process application.
Benchtop instruments can provide fast, accurate nitrogen measurements when quick results are needed.
Ammonia, nitrite and nitrate may naturally occur in bodies of water or be present due to fertilizer runoff, animal waste runoff, failing septic systems, blending with chloraminated water or industrial discharges containing corrosion inhibitors. Therefore, it is important to monitor ammonia, nitrite and nitrate levels in order to guide and optimize treatment.
Titanium (III) ions reduce nitrate and nitrite to ammonia in a basic environment. After centrifugation to remove solids, the ammonia is combined with chlorine to form monochloramine. Monochloramine reacts with salicylate to form 5-aminosalicylate (a green solution), as in the salicylate method for ammonia nitrogen determination (see nitrogen and ammonia).
The organic nitrogen compounds that are present as organically bound nitrogen in the trinegative state are determined in this test. Nitrogen in this form is converted into ammonium salts by the action of sulfuric acid and hydrogen peroxide. The ammonia (both formed and initially present in the sample) is then analyzed by a Nessler Method 8075 and 8038 (LR ammonia). The measurement wavelength is 460 nm for spectrophotometers or 420 nm for colorimeters.
In the simplified TKN ISO approved method, inorganic and organic nitrogen are oxidized to nitrate by digestion with peroxydisulfate. The nitrate ions react with 2,6-dimethylphenol in a solution of sulfuric and phosphoric acid to form a nitrophenol. Oxidized forms of nitrogen in the original sample (nitrite + nitrate, due to sample preservation) are determined in the second test vial and then subtracted, which results in TKN.
An alkaline persulfate digestion converts all forms of nitrogen to nitrate. Sodium metabisulfite is added after the digestion to eliminate interferences from halogen oxides. Under strongly acidic conditions, nitrate reacts with chromotropic acid to nitrate the biphenyl rings at several locations, forming several nitrated products. The nitrated products are measured at 410 nm.
Benchtop/portable:
Inorganic and organic nitrogen compounds are digested with peroxodisulfate and oxidized to nitrate. The nitrate ions react with 2,6-dimethylphenol in a solution of sulfuric and phosphoric acid to form a nitrophenol. The measurement wavelength is 345 nm.
Benchtop:
Inorganic and organic nitrogen compounds are digested with peroxydisulfate and oxidized to nitrate. The nitrate is reduced to nitrite by adding a reducing reagent. The nitrite reacts in an acidic medium with the color reagent to produce a violet azo complex. The measurement wavelength is 546 nm.
Online:
Two-stage advanced oxidation process using hydroxyl radicals. Direct photometric analysis of nitrate after oxidation.
Online:
To learn more about monitoring other forms of nitrogen, visit these related parameter pages: ammonia & ammonium, nitrate & nitrite.
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