Ion-to-electron capacitance of single-walled carbon nanotube layers before and after ion-selective membrane deposition.

The capacitance of the ion-to-electron transducer layer helps to maintain a high potential stability of solid-contact ion-selective electrodes (SC-ISEs), and its estimation is therefore an essential step of SC-ISE characterization. The established chronopotentiometric protocol used to evaluate the capacitance of the single-walled carbon nanotube transducer layer was revised in order to obtain more reliable and better reproducible values and also to allow capacitance to be measured before membrane deposition for electrode manufacturing quality control purposes. The capacitance values measured with the revised method increased linearly with the number of deposited carbon nanotube-based transducer layers and were also found to correlate linearly before and after ion-selective membrane deposition, with correlation slopes close to 1 for nitrate-selective electrodes, to 0.7 and to 0.5 for potassium- and calcium-selective electrodes.