TEMPERATURE COMPENSATION FOR A NITRATE SENSOR

A nearly temperature-independent determination of nitrate in ground wa ter (from 8 to 12-degrees-C) is realize using a chemical sensor measur ing close to its isothermal point. The isothermal point of the nitrate sensor is determined in a strictly symmetrical arrangement of sensor and reference electrode applying different internal reference elements . By varying the composition of the sensor's and the reference electro de's filling solutions the isothermal point is shifted to 0 mV (isothe rmal potential) and 4 X 10(-4) mol/l nitrate (isothermal concentration ). In this case a deviation from 4 X 10)-4) mol/l and 25 ppm nitrate ( maximum value for drinking water proposed by the European Community) i s advantageously measured as a deviation from 0 mV.