Automatic Measurement System for Nitrite and Nitrate in Water Bodies

Abstract

Nitrate and nitrite are reaction products that result, for example, from the application of nitrogenous fertilizers to agricultural land. That part of the nitrogen not absorbed by the plants can pass into the groundwater in the form of nitrate or nitrite. This can also lead to contamination of drinking water via the groundwater, with all its negative side effects. In the present article an automatic system is presented, which performs independently the measurement of nitrate and nitrite at a water body. For the measurement of these parameters commercially available test strips are used, which are evaluated automatically. The determination of the nitrite/nitrate value is based on the Griess reaction which leads to a color change of the test pads depending on the concentration of the analyte. The sample is applied to the test pads with an automated dispenser system and the color change is measured with an RGB sensor. The nitrate/nitrite concentration present can be determined from the R/G ratio and a nomogram. The measuring accuracy of the system meets the requirements of the European Drinking Water Directive for the determination of the nitrate and nitrite value. The limit of detection (LOD) was determined for the self-designed sensor with LOD = 2.003 mg/l for nitrate over a measurement range of 0–50 mg/l nitrate and a LOD of 0.611 mg/l nitrite over a measurement range of 0–10 mg/l nitrite and 0.013 mg/l for a measurement range of 0–1 mg/l nitrite.