Study on Influencing Factors of Measurement of Total Nitrogen by Digestion with UV-Alkaline Potassium Persulfate and Reduction with Hydrazine Sulphate Spectrophotometric Method and Application

The measurement and monitoring of total nitrogen (TN) in water and wastewater were important tasks for environmental engineers, but the key challenge was how to use the technologies in on-line water detection and monitoring. A new method was established according to the improvement of general method which measured total nitrogen in two wavelengths (220 nm and 275 nm). The nitrogenous compounds of water samples were digested and oxidized into nitrate by potassium persulfate at 120degC-124degC in alkaline surroundings couple with ultraviolet (UV) irradiating. An extra step was reduction of the nitrate compounds into nitrite compounds with hydrazine sulphate in reduction solutions. The nitrate compounds were coordinated with N-(l-naphthyl) ethylenediamine dihydrochloride and the color developed, absorbance of samples were determined at 546 nm. The influences of reductive solution, concentration of hydrazine sulphate, pH value, temperature, digestive and reductive time, et aL, were discussed in this paper. When applying the new method in water determination, we found that the determination of total nitrogen by digestion with UV-alkaline potassium persulfate and reduction with hydrazine sulphate spectrophotometric method could fit well with quality control sample and standard samples, and in nature water and waste water determination, the relative standard deviation (RSD) could reach 1.1% and 6.18%, respectively.