Performance evaluation of commercial ion-selective electrodes for hydroponic cultivation system

Abstract

The performance evaluation of commercial ion-selective electrodes (ISE) is important for real-time, ion-based nutrient management in hydroponic crop cultivation systems as the fabrication, ion-sensing membrane’s composition and contamination, storage duration, ion interference, use time, and solution types of ISE cause sensing errors. In this research, the performance of K+, NO3-, and Ca2+ ion-selective electrodes were evaluated in regard to measurement error, potential drift, and calibration for building an effective nutrient management system. A recycle-type aeroponic nutrient management test bench was designed and fabricated. The K+, NO3-, and Ca2+ ISE were attached and tested in the ion-sensing chamber of that test bench. A LabVIEW-coded program and NI-DAQ device were used for data collection. The measurement error percentage was checked in five different levels of nutrient solution. ISE sensors were immersed into a known nutrient level solution for 15 days to check the potential drift trends, and a two-point calibration technique was applied to minimize error effects. A linear relationship was found while testing the measurement error of K+, NO3-, and Ca2+ ISE in five different levels of nutrient solution, where R2 and RMSE were 0.98, 36.86 ppm; 0.99, 22.25 ppm, and 0.99, 12.94 ppm, respectively. The ISE showed continuous upward (R2=0.94, RMSE=54.66 ppm), upward (R2=0.85, RMSE=1.24 ppm), and downward (R2=0.86, RMSE=4.53 ppm) potential drifts, respectively. Two-point calibration to reduce errors showed R2 values of 0.99, 0.99 and 0.99 for K+, NO3-, and Ca2+ ISE, respectively. These results indicated that the performance of commercial ISE needs to be evaluated for improved real-time nutrient ion monitoring in hydroponic cultivation systems. ? 2020 International Society for Horticultural Science. All rights reserved.