A Multi-Sensor for Direct and Simultaneous Monitoring of Changes in the Contents of Four Ionic Components

This paper presents the application of a multi-sensor with a renewable surface based on a carbon black paste modified with ruthenium dioxide hydrate for monitoring the concentration changes of four ionic compounds (nitrate, ammonium, sodium, and calcium). By combining these into one sensor body, analyses can be performed simultaneously, based on a single standard curve, on a small number of available samples. The multi-sensor electrodes were characterized by determining both their electrical parameters, using methods such as chronopotentiometry and electrochemical impedance spectroscopy, and analytical parameters, through a series of potentiometric tests. The electrodes were characterized by high electric charge capacities ranging from 80 µF for the sodium electrode to 257 µF for the nitrate electrode. The tested electrodes showed calibration curve slopes of -51.1 mV/dec for the nitrate electrode, 59.3 mV/dec for the ammonium electrode, 57.0 mV/dec for the sodium electrode, and 26.0 mV/dec for the calcium electrode. The multi-sensor parameters allow for free determination of ions of biological significance in river water samples, soil samples, and plant substrates. The multi-sensor presented in this work can be successfully used to analyze water or plant substrates at home or among commercial crops.