A simple and rapid method is presented for routine analysis of total nitrogen in environmental and waste water samples. Samples are taken into screw top glass bottles, and the bottles are closed with a teflon lined cap after addition of potassium peroxodisulfate and sodium hydroxide solution. After autoclaving at 121°C for 30min, samples are filtered or centrifugated if necessary, and acidified by adding sulfuric acid. Thus all nitrogen compounds in samples are quantitatively oxidized to nitrate. The absorbances at 220nm (A220) and 240nm (A240) are measured, and total nitrogen is determined by calculating the difference between both absorbances (A220-A240). The calibration curves of nitrate follow Beer's law and the applicable range is 0.05-5 mg/l as nitrate nitrogen.
When samples were digested completely, there would be no interference of organic chemicals. Moreover interferences of inorganic chemicals at levels occurring in waste waters were eliminated by subtracting A240 from A220. This proposed method was compared favourably with the Kjeldahl digestion method for river and waste water samples, and with the determination by T-N analyser for sea water samples.