Development of the simultaneous determination of anionic and cationic nutrients in hydroponic solutions using...

In hydroponic cultivation, pH and electrical conductivity are currently widely used as indicators for nutrient management, whereas the concentrations and compositions of individual ions (NO₃^‒, NO₂^‒, NH₄⁺, H₂PO₄^‒/HPO₄^2‒, K⁺) are not precisely monitored. To reduce the environmental load and nutrient costs in future hydroponics, individual fertilization management based on effective and detailed monitoring of nutrients is required, necessitating accurate evaluation of nutrient levels. In this study, we describe the development and application of ion exclusion/cation exchange chromatography (IEC/CEC) with a neutral eluent (40 mM sodium acetate, and 0.5 mM 18-crown-6, pH 7.71) for simultaneous separation of ionic nutrients in a hydroponic fertilizer solution. These problems of the degradation of the separation column due to the precipitation of metal ion species under alkaline elution condition and the oxidation of NO₂^‒ to NO₃^‒ encountered under acidic eluent used in previously reported chromatographic studies were avoided while ensuring the base gel stability by using a polymer-based zwitterionic exchanger with neutral eluent. In addition, the developed IEC/CEC method was successfully applied to monitor the temporal evolution of the amount of target ionic nutrients in hydroponic solutions.