Abstract
A solid state ion sensor module has been developed and evaluated for hydroponic nutrients analysis. The sensor module consisted of five ion-selective electrodes (ISE) fabricated by screen-printing technology. The electrochemical responses of ion sensors for nitrate, ammonium, potassium, calcium, and pH were measured with specially designed 7-channel low voltage signal transducers. The analytical characteristics of the sensors were comparable with those of conventional ISE sensors. The solid state ion sensors exhibit linear relationships over five concentration decades. Detection limit of the sensors were $5.6{\times}10^{-5}{\sim}1.6{\times}10^{-7}M$ depends on ions. Performance test results showed that relative errors of measured ion concentrations were less than 5% for $NO_3{^-},\;K^+,\;Ca^{2+}$ ion, and pH. The concentration of $NO_3{^-},\;NH_4{^+},\;K^+,\;Ca^{2+}$, and pH ion in standard solution and nutrient solutions could be determined by direct potentiometric measurements without any conditioning before measurements.
