Nitrate‐nitrogen determination—a critical review

This paper reviews the published methods of nitrate‐nitrogen (NO3‐N) determination with the objective to assess their applicability to soil and plant tissue anarysis. The methods are separated into three categories on the basis of the analytical approach utilized for NO3‐N determination. Strengths and weaknesses of the methods are discussed. The first analytical approach utilitizes direct measurement of NO3‐N by the following methods: (a) colorimetric (after a color producing reaction with NO3‐N), (b) potentiometric, (c) absorption of UV radiation by NO3‐N in a complex matrix, (d) transnitration of salicylic acid, and (e) chromatographic (separation and measurement of NO3‐N) methods. The second approach is based on the reduction of NO3‐N to nitrite‐nitrogen (NO2‐N), ammonium‐nitrogen (NH4‐N), or nitric oxide and measurement of the reduction product. When NO3‐N is reduced to NO2‐N, the measurement may be achieved by (a) colorimetric, (b) fluorimetric, (c) coulometric, and (d) catalytic kinetic methods. When NO3‐N is reduced to NH4‐N, the measurement is done by (a) colorimetric (after a color producing reaction with NH4), (b) potentiometric, (c) steam distillation, and (d) gas diffussion conductimetric methods. A chemiluminescence detection method is utilized when NO3‐N is reduced to nitric oxide. The third approach determines NO3‐N concentration by measuring the change in the concentration of the chemical species that react with NO3‐N and form a complex.