Stability and reproducibility study for the development of a potentiometric nitrate sensor for in-situ use

This study investigates the stability and reproducibility of a potentiometric nitrate sensor in all-solid-state configuration, consisting of a screen-printed graphite electrode, coated with electropolymerized polypyrrole as solid contact material, and covered by a TDMA-based ion-selective membrane. Special attention is given to the long-term stability, depending on storage and conditioning conditions as the most important factors for the applicability of the sensor. In particular, regression lines from calibration procedures, performed over a period of up to three months, were analyzed to evaluate the sensor performance. The sensor demonstrated superior stability, with minimal, nearly parallel shifts between regression lines. Notably, the sensor retained its ability to reproduce signals accurately even after one-month periods of dry storage, provided that the applied conditioning period was sufficiently long. The sensor was successfully applied for nitrate detection in drinking water samples, with a reproducibility of ± 3 mg/L, making it a promising candidate for real-time nitrate sensing applications. In all stages of the experiments, the sensor performance was compared with that of an all-solid-state sensor system, consisting of a gold electrode coated with poly(3-octylthiophene-2,5-diyl) and molybdenum disulfide nanocomposites as solid contact material.