Analytical Sciences

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

Yuko FUKAO, Yuki KITAZUMI, Kenji KANO, and Osamu SHIRAI

Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo, Kyoto 606-8502, Japan

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.

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