Rapid Constant Potential Capacitive Measurements with Solid-Contact Ion-Selective Electrodes Coupled to Electronic...

Area of Science:

• Electrochemistry
• Sensing Technology
• Materials Science

Background:

• Solid-contact ion-selective electrodes (SC-ISE) offer sensitive ion activity measurements via capacitive readout.
• Traditional SC-ISE methods suffer from long measurement times and baseline drifts, hindering practical application.
• Current transient integration provides a charge vs. logarithmic activity relationship, potentially more sensitive than potentiometry.

Purpose of the Study:

• To overcome the limitations of long measurement times and baseline drifts in SC-ISE.
• To enhance the sensitivity and practicality of capacitive readout for SC-ISE.
• To demonstrate a novel method for improving SC-ISE performance using an external capacitor.

Main Methods:

• SC-ISE were connected in series with an electronic capacitor, using pH probes as a model system.
• Kirchhoff's law was applied to determine appropriate capacitance values that dominate the cell impedance.
• Two ion-to-electron transducing materials, functionalized single-wall carbon nanotubes (f-SWCNTs) and poly(3-octylthiophene) (POT), were investigated.

Main Results:

• Adding an electronic capacitor significantly reduced measurement time to under 10 seconds.
• The f-SWCNT transducer supported a wide capacitance range (up to 100 μF), while POT required a narrower range (1-4.7 μF).
• Rapid decay of response current to zero, due to capacitor behavior, enabled practical charge determination.

Conclusions:

• Integrating an electronic capacitor in series with SC-ISE overcomes previous limitations, enabling rapid and sensitive ion activity measurements.
• The f-SWCNT transducer demonstrates robust performance across a broad range of added capacitances.
• This approach significantly advances the applicability of capacitive readout for SC-ISE in various sensing applications.