Hydrogels Doped with Redox Buffers as Transducers for Ion-Selective Electrodes

Area of Science:

• Electrochemistry
• Analytical Chemistry
• Materials Science

Background:

• Solid-contact ion-selective electrodes (ISEs) often exhibit potential drift due to unstable phase boundary potentials at the interface between the sensing membrane and an unintentional water layer.
• The reproducibility and long-term stability of ISEs utilizing miniaturized inner filling solutions with hydrogels and hydrophilic electrolytes require further investigation.

Purpose of the Study:

• To investigate the electrode-to-electrode reproducibility and long-term electromotive force (emf) stability of solid-contact ISEs employing a hydrogel-based inner filling solution.
• To evaluate the performance of these ISEs with both plasticized PVC and hydrophilic ion-exchange sensing membranes.

Main Methods:

• Fabrication of solid-contact ISEs with a miniaturized inner filling solution containing a hydrogel and hydrophilic electrolyte.
• Incorporation of a hydrophilic redox buffer (ferrocyanide/ferricyanide) to stabilize the potential between the hydrogel and the underlying electron conductor.
• Testing of electrodes with both plasticized PVC and hydrophilic ion-exchange sensing membranes to assess reproducibility and long-term drift.

Main Results:

• Electrodes with plasticized PVC membranes demonstrated excellent initial potential (E0) reproducibility of ±1.1 mV or better.
• Electrodes with hydrophilic ion-exchange membranes showed slightly larger, but still acceptable, variability in initial potential.
• Long-term drift assessments indicated that osmotic pressure had an insignificant effect on PVC membranes and a minimal effect on hydrophilic membranes.

Conclusions:

• Solid-contact ISEs with hydrogel-based inner filling solutions offer high electrode-to-electrode reproducibility and improved long-term emf stability.
• The use of a hydrophilic redox buffer effectively controls potential, mitigating drift issues common in conventional solid-contact ISEs.
• These findings suggest a promising approach for developing more reliable and stable electrochemical sensors.