Rapid and selective detection of K in cigarette paper: The use of solid-contact polymer membrane electrodes based on ZnCoO-loaded hollow carbon nanospheres.

In comparison to the classical liquid-contact ion-selective electrode (LC-ISE), the potential stability remains one of the major challenges currently faced by the solid-contact ion-selective electrode (SC-ISE). This challenge can be addressed by introducing a conducting layer between the conductive substrate and the polymer membrane to stabilize the potential output. In this paper, hollow carbon nanospheres loaded with zinc cobaltate nanoparticles (ZnCoO@HCNs) were synthesized by using a one-pot method, which served as an ion-electron conducting layer between the potassium ion-selective polymer membrane and the conductive glassy carbon substrate. Electrochemical impedance spectroscopy (EIS) and chronopotentiometry tests demonstrated a high capacitance and excellent potential stability for the solid-contact potassium ion-selective electrode (K/SC-ISE). Water layer tests further confirmed that ZnCoO@HCNs exhibited strong hydrophobicity, effectively preventing the formation of water contact layers at the electrode/membrane interface, thereby ensuring a highly stable signal-response. Under the optimized conditions, the prepared K/SC-ISE showed a good linear response in the concentration range of 1.0 × 10-1.0 × 10 mol/L with a Nernst slope of 56.03 ± 0.55 mV/decade. The detection limit was calculated to be 6.16 × 10 mol/L. Additionally, the electrode demonstrated excellent selectivity, stability, and a long lifetime of over 24 months. Finally, the electrode was successfully applied to the on-site detection of K in actual cigarette paper samples at the factory workshop, yielding results consistent with those using ion chromatography, highlighting its broad application prospect.