Construction of nitrate-selective electrodes and monitoring of nitrates in hydroponic solutions

Abstract

A liquid-membrane type nitrate-selective electrode was constructed, in which the responding membrane contained polyvinylchloride, o-nitrophenyloctylether and tetraheptylammonium nitrate. The NO 3- -selective electrode displayed a linear response to the concentration of NO 3- with a Nernstian slope of -53.3 ± 1.0 mV decade -1 , in the 10 -5 - 10 -1 mol dm 3- (M) NO 3- concentration range. The NO 3- detection limit was about 10 -6 M. The electrochemical response of this electrode was stable for more than 30 days. Measurements performed using the NO 3-- sensor indicated that in the presence of green plants, the concentration of NO 3- in a hydroponic solution decreased from 0.20 to 0.05 mM over a three-day period.