Spectrophotometric Determination of Nitrate-Nitrogen Using 1-Naphthol-8-sulfonic Acid and Its Application to Total Nitrogen Analysis

Abstract

A spectrophotometric method for the determination of nitrate-nitrogen was developed based on the reaction of nitrate with 1-naphthol-8-sulfonic acid in the presence of sulfuric acid and chloride. A calibration curve based on the absorbance at 350 nm against a reagent-blank reference was linear in the concentration range of 0∼6.00 μg/ml of nitrate-nitrogen. The color development can probably be ascribed to the formation of a nitroso-derivative of the parent acid caused by nitrosyl chloride resulting from the reaction of nitrate and chloride under strongly acidic conditions. The interference of common inorganic anions and cations was not serious, expect for nitrite, which gave a high positive error. This method was able to measure nitrate-nitrogen in well water and river water. The results were in good agreement with those obtained by an ion chromatographic method. In addition, this method gave satisfactory results in the determination of total nitrogen in sewage water, and was also useful for a semi-quantitative analysis of nitrate based on the strength of the developed color.