Superhydrophobic polyaniline solid contact for potential stability improvement of NH4+-selective electrode

Potential stability and reproducibility of solid-contact ion-selective electrodes (SC-ISEs) are key to ensure reliable accuracy of actual water sample monitoring. However, undesirable water layer formed at interface of SCs and ion-selective membranes inevitably changes the interfacial potential. Here a superhydrophobic polyaniline (PANI) SC is presented to improve potential response of NH4+-ISE. Electrodeposition methods are used to control PANI growth and perfluorooctanoic acid co-doping, forming PANI SCs with different wettabilities. Though constructed SC-NH4+-ISEs show detection linear ranges from 10-5 to 10-1 M, superhydrophobic SC-ISE has a slope (58.07 mV/dec) closest to the ideal Nernstian slope. Importantly, superhydrophobic SC greatly inhibits water layer formation and enables SC-NH4+-ISE to have a very stable potential response. Potential drift is only 13.6±3.2 µV/h for 12 h continuous measurement and standard deviation of the standard potential is 0.96 mV (n = 3), which are 55.7 and 5.4 times lower than those of unmodified SC-ISE, respectively. Moreover, superhydrophobic SC-ISE exhibits excellent potential stability against external interferences and even during actual wastewater monitoring. Once water layer is formed in unmodified SC-ISE, inaccuracy of measured NH4+ concentrations in actual wastewater reaches ca. 37%. This study demonstrates that superhydrophobic SC can efficiently improve potential response of SC-ISEs.