Feasibility Study of an All-solid-state ISE Using Quaternary Ammonium Compounds for Soil Nitrate-nitrogen Fast Determination

Abstract

In recent years, the prolific usage of nitrogenous fertilizers in extensive agricultural area of China has resulted in inefficient nitrogen usage, environmental pollution and the degradation of the soil fertility. As such, a rapid, low-cost and reliable detection method for soil nitrate is urgently needed. Traditional ISE electrodes operated on ions diffusing across an ion-selective thin membrane in a solution to an internal reference electrode. These ISE electrodes were usually not conducive to system miniaturization. In order to improve miniaturization, an all-solid-state ISE coated with a polymeric polyvinyl (PVC) membrane using quaternary ammonium compounds as electroactive material was developed in this paper. The membrane was deposited onto the surface of a glassy carbon electrode after polishing and cleaning. Membrane synthesis variables were used to optimize the potentiometric response of the electrodes and to maximize the sensitivity, stability and selectivity of nitrate over potentially interfere anions. With optimized membrane deposition parameters, the potentiometric responses of these PVC ISE electrodes were found to follow a quasi-Nernst response over a linear range of 10-3~10-1mol/L. The detection limit of these PVC ISE electrodes was 1.0×10-4 mol/L. The potentiometric slopes remained fairly constant and were found to vary from -46 mV/decade to -40 mV/decade. A detection response time of less than 20 seconds was observed in these electrodes.