Flow-injection biamperometric determination of nitrate (by photoreduction) and nitrite with the NO2-/I- reaction

An unsegmented continuous-flow method for the determination of nitrite and nitrate is proposed. Nitrate is photoreduced by UV irradiation with a low-pressure 8 w mercury lamp. The nitrite in the sample and that resulting from the photoreduction of nitrate are used to oxidize iodide ion. Tri-iodide thus formed is detected biamperometrically in excess iodide by using a flow-cell furnished with two platinum electrodes polarized at 100 mV. The limits of detection, throughput and reproducibility (n=26) thus achieved for nitrite and nitrate are 25 and 50 mu g l(-1), 27 and 25 h(-1), and 1.2 and 1.6%, respectively. The proposed method was used to determine nitrate and nitrite in natural waters, waste waters, soils, meat products and fertilizers. (C) 1998 Elsevier Science B.V.