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Innovative solid-state microelectrode for nitrite determination in a nitrifying granule.

Nitrite is an intermediate of both nitrification and denitrification in biological removal of nitrogen from wastewater, and in situ measurement of nitrite concentration in a biofilm or microbial granules is highly desirable. However, a solid-state microelectrode for nitrite determination is not available yet In this work, a solid-state microelectrode was manufactured through electrochemical codeposition of Pt--Fe nanoparticles on a gold microelectrode fabricated using photolithography for in situ nitrite determination. This gold-based microelectrode could be used as a more cost-effective, efficient, and reliable alternative to the liquid membrane microelectrode. Nanoparticles with an average diameter of 50 nm were observed on the surface of the chemically modified electrode. A sigmoid peak at ca. 0.7 V (vs Ag/AgCl) was found on the linear sweep voltammogram in nitrite solutions by using the fabricated microelectrode. The peak height of the first-order derivative of the sigmoid peak was proportional to the nitrite concentration of 0.001--0.05 M and could be used for quantitative determination of nitrite. The detection limits (S/N = 3) were approximately 3 x 10(-5) M. The nitrite microprofiles of aerobic granules from a nitrifying reactor were measured with the microelectrode to demonstrate its potential applications with high spatial resolution.