A simple manually rotated paper-based analytical device with electrochemical sensors for the determination of nitrite and nitrate.

A user-friendly, rotational paper-based device integrating electrochemical sensors is presented. This innovative device accurately determines nitrite and nitrate ions. Its circular design facilitates the simultaneous detection of both ions. The rotational analytical platform consists of a paper disc that accommodates samples introduced via plastic pipettes. The front side of the disc contains the electrochemical sensors, while the back features a pattern for sample loading. These sensors are specifically designed to detect nitrite and nitrate ions in the sample. Nitrite is determined directly at a working potential of +0.6 V, whereas nitrate is measured after its reduction to nitrite using zinc dust. Moreover, the sensing electrodes are screen-printed carbon electrodes modified with N-doped multiwalled carbon nanotubes (N-MWCNTs) and copper(II) phthalocyanine (CuPc) to enhance sensitivity for nitrite oxidation. This simple device provides a linear range of 50-1000 μM for the simultaneous determination of nitrite and nitrate ions, with detection limits of 10.0 and 20.0 μM, respectively. Furthermore, a manually rotated acrylic plate is employed during sample preparation to facilitate the reduction of nitrate to nitrite. The analytical protocol has been successfully applied to meat samples, and this integrated, portable device shows great potential for rapid, on-site determination of nitrite and nitrate ions in food samples.