Redox Buffer Capacity of Ion-Selective Electrode Solid Contacts Doped with Organometallic Complexes

Area of Science:

• Electrochemistry
• Analytical Chemistry
• Materials Science

Background:

• Traditional ion-selective electrodes (ISEs) use inner filling solutions, limiting miniaturization.
• Solid-contact ISEs offer advantages for miniaturization and mass production.
• Reproducible calibration-free measurements require stable phase boundary potentials.

Purpose of the Study:

• To introduce the theory and experimental data for controlling phase boundary potentials in solid-contact ISEs.
• To investigate the impact of redox buffers on phase boundary potential stability.
• To evaluate the influence of weighing errors, impurities, and interferents on electrode performance.

Main Methods:

• Theoretical modeling of phase boundary potential dependence on redox species.
• Experimental validation using solid contacts doped with Co(III)/Co(II), Ru(II), Fe(II), and Os(II) compounds.
• Analysis of the effects of redox-active impurities and concentration ratios.

Main Results:

• Phase boundary potential shows minimal dependence on the ratio of oxidized/reduced compounds if they are not a redox couple.
• Small redox-active impurities significantly shift the phase boundary potential.
• In-batch reproducibility is observed for solid contacts with single redox species, attributed to impurities.

Conclusions:

• Calibration-free sensing with solid-contact ISEs is best achieved using redox buffers with controlled concentrations of both reduced and oxidized species.
• Precise control over redox buffer composition is crucial for reliable and reproducible measurements.
• The presence of redox-active impurities can mask the true behavior of the redox system.