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.