Analytical Sciences

Microfluidic Polymer Chip with an Embedded Ion-Selective Electrode Detector for Nitrate-Ion Assay in Environmental Samples

Takashi MASADOME,* Kazuki NAKAMURA,* Daisuke IIJIMA,* Osamu HORIUCHI,* Benjaporn TOSSANAITADA,* Shin-ichi WAKIDA,** and Toshihiko IMATO***

*Department of Applied Chemistry, Faculty of Engineering, Shibaura Institute of Technology, Toyosu, Koto, Tokyo 135-8548, Japan
**Health Device Research Institute, Human Stress Signal Research Center (HSS), National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan
***Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, Fukuoka 819-0395, Japan

A nitrate ion-selective electrode (NO_3⁻-ISE) has been developed based on tetradodecylammonium bromide as an anion exchanger and 2-nitrophenyl octyl ether as a plasticizer. The NO_3⁻-ISE shows an almost Nernstian response to nitrate ion over a concentration range between 1.0 × 10⁻⁶ and 1.0 × 10⁻¹ M, with an anionic slope of −57.7 ± 0.7 mV/decade. The selectivity coefficients of the NO_3⁻-ISE for nitrate ion against chloride and sulfate (log k^pot_NO3⁻Cl⁻ = −2.42 and log k^pot_{NO3⁻SO4²⁻} = −4.33) were obtained. A microfluidic polymer chip was fabricated using polystyrene plates and stainless-steel wires as a template for the channel. The microfluidic polymer chip is composed of a mixing chip and a NO_3⁻-ISE detector chip. The microfluidic polymer chip, integrated with a NO_3⁻-ISE detector consisting of the NO_3⁻-ISE and a Na⁺-ISE as a reference electrode, showed an almost Nernstian response to nitrate ion over a concentration range between 1.0 × 10⁻⁵ and 1.0 × 10⁻¹ M, with an anionic slope of −54.3 ± 1.3 mV/decade. The microfluidic polymer chip was then applied to the determination of nitrate ion in environmental water samples, such as a tap water, a well-water sample and water for agricultural use.

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