Nitrites in soil are readily oxidized to nitrate. The nitrite concentration is determined by diazotizing with sulfanilamide and coupling with NED dihydrochloride to form a colored azo dye that is measured colorimetrically. Nitrate is determined potentiometrically using an NH3 gas-sensing electrode after nitrate is reduced to NH3 by a titanous chloride reagent. Measure separately and subtract. The nitrite concentrations is determined by diazotizing with sulfanilamide and coupling with NED dihydrochloride to form a colored azo dye that is measured colorimetrically.
Reaction produces indophenol, an intensely blue compound.