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Detection of nitrite and nitrate with the Griess method. Sulfanilamide reacts with NO2− in acidic pH to yield a diazonium intermediate that subsequently reacts with N-(1-naphthyl)ethylenediamine to yield the intensely colored Griess product with absorption maximum at 540 nm. NO3− can be converted to NO2− with vanadium chloride or NO3− reductase to allow both NO3− and NO2− to be measured.
