The Nitrate Ion Electrode provides the primary measurement, while a second electrode measures the Chloride ions in the sample. The chloride ion, due to its similar size and charge to the nitrate ion, causes a positive interference in the measurement. The Chloride Ion Electrode measures the amount of chloride ion present in the sample and the transmitter subtracts the appropriate amount of signal from the Nitrate Measurement.
An optional pH or NH4+electrode is also available in the HYDRA®- NO3 sensor. While not required for the measurement an optional pH or Ammonium electrode can provide valuable information about the process. Temperature is measured and used to compensate each of the measurements.