A Systematic Approach to Nitrate-Selective Molecular Cages based Synthetic Ionophore for Potentiometric Sensing Applications

Abstract

Nitrate ions are prevalent pollutants in water and soil, posing risks to human health and the environment therefore it is important to monitor nitrate levels in various water and soil sources due to their high-risk potential. Electrochemical analysis offers advantages such as affordable, user-friendly, and real-time measurements for NO3- through potentiometric ion-selective electrodes (ISEs) that quantify ion concentrations. Centre of this technology is the ionophore, a critical component facilitating the selective and precise measurement of specific ions in solution. Routinely, ionophores have been derived from natural sources; however, these natural ionophores are limited in terms of the ions they can detect and are not readily modifiable. Synthetic ionophores, on the other hand, can be designed with high selectivity and sensitivity for specific ions, making them ideal candidates for use in ion-selective electrodes. In this context, we present a systematic approach to a molecular cage as an ionophore for nitrate ions. By varying the molecular structure and, therefore, the size of cage molecules, we aimed to adjust the interaction between host-cage molecules and the guest-NO3- ions. NO3- ions selective binding capacity of six different synthetic ionophore candidates was evaluated potentiometrically. The electrode that provides the optimal interaction cage-NO3- exhibited a linear response within the concentration range of 1.0×10-5 to 1.0×10-1 M, with a high coefficient of determination (R2 = 0.9971) and a slope of -53.1 ± 1.4 mV dec-1. The calculated limit of detection for the NO3- selective electrode was determined to be 7.5×10-6 M.