Temperature-Dependent Dielectric Response of Aqueous Solutions to Presence of Nitrate Ions.

Dielectric probes are widely used in agricultural systems and environmental monitoring to estimate field variables of interest, particularly soil water content and salinity. However the dielectric and conductive nature of soil aqueous phase can vary depending on measurement frequency, temperature and ion type and concentrations presented in the solution.  Analyzing the dielectric response of ion-water mixture at multiple frequencies can yield ion-specific information which can be used in dielectric sensing to evaluate ionic composition of soil solution. This new feature can add an enormous value to current dielectric measurement methods, particularly in agricultural applications where in-situ measurement of nitrate ions remains unsolved problem. Hence, the goal of the study was to investigate potential to measure nitrate concentration in aqueous solutions through multi-frequency dielectric measurement. Temperature-dependent dielectric responses of the solutions were measure at a frequency range of 5 Hz to 13 MHz using an LF impedance analyzer and a liquid dielectric test fixture. Chlorine ions at different concentration were introduced into the nitrate solutions during the study to understand an effect of background ions on dielectric measurement in order to separate it from the nitrate-induced response.