Microfluidic polymer chip with an embedded ion-selective electrode detector for nitrate-ion assay in environmental samples

A nitrate ion-selective electrode (NO₃-_-ISE) has been developed based on tetradodecylammonium bromide as an anion exchanger and 2-nitrophenyl octyl ether as a plasticizer. The NO₃-_-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 NO₃-_-ISE for nitrate ion against chloride and sulfate 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 NO₃-_-ISE detector chip. The microfluidic polymer chip, integrated with a NO₃-_-ISE detector consisting of the NO₃-_-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. 2010