Alternative coulometric signal readout based on a solid-contact ion-selective electrode for detection of nitrate

• Published in: Analytica chimica acta 2020-09, Vol.1129, p.136-142
• Main Authors: Wang, Hemin, Yuan, Baiqing, Yin, Tanji, Qin, Wei
• Format: Article
• Language: English
• Subjects: Coulometric signal; Electrical double layer capacitance; NO3; Ordered mesoporous carbon; Solid-contact ion-selective electrode
• ISSN: 0003-2670; 1873-4324
• DOI: 10.1016/j.aca.2020.07.019

Traditional potentiometric NO3−-selective electrodes suffer from a fundamental limitation of the Nernst slope (59.1 mV/dec at 25 °C) due to the relationship between the potential and the logarithmic of ionic activity. Herein, a coulometric signal readout is proposed instead of the potentiometric response for detection of NO3− based on an ordered mesoporous carbon (OMC)-based solid-contact ion-selective electrode (ISE). The mechanism for obtaining the coulometric signal is based on the electrical double layer capacitance of OMC compensating the potential change at the ion-selective membrane/solution interface during the measurements under the control of a constant applied potential. Under the optimized conditions, the coulometric signal for the OMC-based solid-contact NO3−-ISE shows two linear responses in the activity range of 1.0 × 10−6-8.0 × 10−6 M and 8.0 × 10−6-8.0 × 10−4 M, and the detection limit is 4.0 × 10−7 M (3σ/s). The proposed coulometric response also shows excellent reproducibility and stability in the presence of O2 and CO2 and light on/off. Additionally, the coulometric response shows acceptable and reliable results for detection of NO3− in mineral water as compared to the traditional potentiometric response and the ion chromatography. This work provides a promising alternative signal readout for detection of ions by using solid-contact ion-selective electrodes. [Display omitted] •A coulometric signal readout is proposed based on OMC-based solid-contact NO3−-ISE.•The signal depends on OMC with electrical double layer capacitance as solid contact.•The coulometric signal for NO3−-ISE is robust to O2, CO2 and light interferences.