Construction of Nitrate-selective Electrodes and Monitoring of Nitrates in Hydroponic Solutions

A liquid-membrane type nitrate-selective electrode was constructed, in which the responding membrane contained polyvinylchloride, o-nitrophenyloctylether and tetraheptylammonium nitrate. The NO₃^--selective electrode displayed a linear response to the concentration of NO₃^- with a Nernstian slope of -53.3 ± 1.0 mV decade^-1, in the 10^-5 - 10^-1 mol dm^-3 (M) NO₃^- concentration range. The NO₃^- detection limit was about 10^-6 M. The electrochemical response of this electrode was stable for more than 30 days. Measurements performed using the NO₃^--sensor indicated that in the presence of green plants, the concentration of NO₃^- in a hydroponic solution decreased from 0.20 to 0.05 mM over a three-day period.