Miniature Ion-selective Electrodes with Mesoporous Carbon Black as Solid Contact

Herein, we demonstrated miniature solid-contact ion-selective electrodes (ISEs) using a commercial mesoporous carbon black (MCB) as ion-to-electron transducer. MCB is attractive in its high surface area, good conductivity, relative low cost and availability. ISEs for potassium (K+) and nitrate (NO3-) ions were prepared by subsequently coating the sealed glass capillaries (1.5 mm) with MCB and ion-selective membranes. Addition of MCB substantially stabilized electrode response by providing adequate double-layer capacitance and lowering resistance by more than 100x compared to the coated-wire electrodes. The electrodes exhibited near-Nernstian slopes of 59.6 (K+ ionophore), 57.8 (K+ ion-exchanger) and -54.8 (NO3- ion-exchanger) with standard solutions in the range of 10(-5) to 10(-1) M. Fast response (similar to 10 s) and reproducible sensitivities were also obtained in a mixed electrolyte containing interfering ions, although with a baseline drift of 2-10 mV/day in the long term. Importantly, the electrodes can be simply stored in air between measurements and used directly without conditioning in solutions. With simple fabrication and free maintenance, these sensors offer a low cost and convenient alternative to bulk ISEs, especially when sample volumes or space are limited.

Automated summary

Miniature solid-contact ion-selective electrodes using commercial mesoporous carbon black as ion-to-electron transducer showed stable electrode response, near-Nernstian slopes, and fast response in mixed electrolytes with interfering ions. These electrodes can be stored in air and used directly without conditioning, offering a low cost and convenient alternative to bulk ISEs.