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

Abstract

While ion-selective electrodes (ISEs) with inner filling solutions are used widely, solid-contact ISEs are better suited for miniaturization and mass manufacturing. Calibration-free measurements with such electrodes require the reproducible control of the phase boundary potential between the ion-selective membrane and the underlying electron conductor. The most promising approach to achieve this goal is based on redox buffers incorporated into the ion-selective membrane. Here we introduce the theory and present experimental data for Co(III), Co(II), Ru(II), Fe(II), and Os(II) compounds that show quantitatively how the phase boundary potential at a solid contact doped with redox-active compounds is affected by weighing errors, reagent impurities, and redox-active interferents. Perhaps surprisingly, theory predicts that there is only a minimal dependence of the phase boundary potential on the ratio of the concentrations of a pure oxidized and a pure reduced compounds if those two compounds are not a redox couple. However, theory predicts that even small redox-active impurities of those compounds shift the phase boundary potential drastically. Experimentally, a surprisingly good in-batch reproducibility was observed by us and others for solid contacts prepared to contain either only the reduced or only the oxidized species of a redox couple. This can be explained by redox-active impurities and is unlikely to be repeatable when different suppliers of reagents are used or long-term experiments are performed. This work confirms that the preferred approach to calibration-free sensing is based on redox buffers that comprise the reduced and oxidized species of a redox couple in well-controlled concentrations.

Recent advances in potentiometric biosensors

“…Meanwhile, solidstate reference electrodes have been rationally designed and manufactured [19e23]. Currently, several groups including the Bühlmann [24], Bobacka [25], Bakker [26], Lindner [27], Gyurcs anyi [28], Qin [29], Lindfors [30], Crespo [31], and Michalska [32] group are active in this field. Recently, the introduction of nanopore show promises for potentiometric sensing applications [33e35].…”

Lipophilic Multi‐walled Carbon Nanotube‐based Solid Contact Potassium Ion‐selective Electrodes with Reproducible Standard Potentials. A Comparative Study

“…Therefore, this aspect gained lately a lot of interest beside ensuring all other criteria for optimal potentiometric behavior of SCISEs. Pertinent solutions included the adjustment of the potential through adjusting the ratio of a redox couple or in general redox compounds as well as through prepolarization of the SCISEs . The latter is clearly a more generic approach and while it has been used mostly with conducting polymer‐based SC materials , we become interested on its feasibility for capacitive contacts and its comparison with state of the art conducting polymer based solid contacts.…”

Determination of the Total Phenolic Content in Wine Samples Using Potentiometric Method Based on Permanganate Ion as an Indicator

“…Recently, it has been realized fully that minor ionic fluxes in certain concentration ranges of the inner solution have an important role in determining the potentiometric response [27,28]. The effect of indicator permanganate ions on the detection sensitivity was investigated here and the result is illustrated in Figure 3.…”