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A Simple Spectrophotometric Determination of Nitrate in Water, Resin, and Soil Extracts

Yang, J. E., Kim, J. J., Skogley, E. O., Schaff, B. E.
Soil Science Society of America journal 1998 v.62 no.4 pp. 1108-1115
colorimetry, sodium salicylate, chemical analysis, nitrate nitrogen, rapid methods, soil analysis, water, accuracy
Nitrate is one of the most important chemicals in agricultural and environmental management. Most methods for NO₃ analysis, however, require expensive equipment or complicated procedures. The objective of this study was to develop a simple, rapid, accurate procedure for NO₃ analysis that can be conducted in laboratories worldwide, without the need for specialized equipment. We based our studies on a colorimetric method that involves electrophilic aromatic substitution (nitration) between nitronium and salicylate. The simplified procedure was tested for NO₃ analysis of water, soil, and resin extracts. Only 1 mL of sample containing 0 to 4 mg NO₃-N L⁻¹ is required, and a single solution (TRI solution made as a mixture of sodium salicylate [2-hydroxybenzoic acid monosodium salt], NaCl, and ammonium sulfamate [sulfamic acid monoammonium salt]) is used for color development. The detection limit is 0.1 µg NO₃-N, with linearity up to 4 µg NO₃-N in a final volume of 11 mL. Evaporation of the sample may be done in several ways to remove water from reactants, as long as the temperature for activiation of nitration is attained. Resin extracts from 2 M HCl required neutralization with 2 M NaOH prior to analysis, and soil extracts from 1 M KCl provided more uniform results than from 2 M KCl. Results from all types of solution samples were highly significantly correlated with those by the automated Cd-reduction method. This simplified sodium salicylate procedure (SSP) for NO₃ analysis is simple, reproducible, and it requires only inexpensive equipment. Contribution no. J5109 from Montana Agric. Exp. Stn. and Kangwon Natl. Univ.