Determination of Total Nitrogen in Water by OnLine Digestion with Flow Injection

An automatic method for the determination of total nitrogen in water by flow injection with on-line digestion was developed.The sample was digested with potassium persulphate in basic medium under electric heating and UV radiation.The organic and inorganic nitrogen compounds were oxidized to nitrate with the efficiency of 93.0%—108.5%.Nitrate was reduced to nitrite in a copperized cadmium column,and reacted with N-(1-naphthyl)ethylenediamine dihydrochloride and sulfanilamide to form azo dye and formed a color complex with maximum absorption peak at 540nm.The calibration curve was linear in the range of 20.0—2000.0μg·L-1(r≥0.9995).Detection limit was 8.3μg·L-1.The relative standard deviation was 0.8%—1.6% with the sample throughput of 35 samples every one hour.Total nitrogen was determined in the real samples of river water,underground water and tap water with the recovery of nitrate of 95.9%—107.3%.There was no difference between FIA and batch method(GB 11894-89) through the determination of the total nitrogen in waste water.