Abstract
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.Graphical abstract
Highlights
The need to miniaturize potentiometric sensors gave rise to the development of solid-contact ion-selective electrodes (SC-ISEs) and triggered the search for ideal transducer materials
The potential stability and reproducibility of SC-ISEs are known to be determined by the properties of the ion-toelectron transducer layer
The estimation of its capacitance has become an essential part of its characterization, as demonstrated by the fact that 30 of the 46 publications dedicated to SC-ISEs that were cited in a review
Summary
The need to miniaturize potentiometric sensors gave rise to the development of SC-ISEs and triggered the search for ideal transducer materials. The potential stability and reproducibility of SC-ISEs are known to be determined by the properties of the ion-toelectron transducer layer. Within this context, the estimation of its capacitance has become an essential part of its characterization, as demonstrated by the fact that 30 of the 46 publications dedicated to SC-ISEs that were cited in a review. The capacitance of a transducer layer of SC-ISEs is usually determined by means of electrochemical impedance spectroscopy or chronopotentiometry The latter protocol, introduced by Johan Bobacka in 1999 [2], applies consecutive positive and negative current pulses of the same amplitude to the SC-ISE and monitors the resulting potential drift, and it is often preferred over the former methodology owing to its more straightforward data treatment approach
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