Potential Reproducibility of Potassium-Selective Electrodes Having Perfluorinated Alkanoate Side Chain Functionalized Poly(3,4-ethylenedioxytiophene) as a Hydrophobic Solid Contact

Abstract

The irreproducibility of the standard potential (E°) is probably the last major challenge for the commercialization of solid-contact ion-selective electrodes (SCISEs) as single-use or wearable sensors. To overcome this issue, we are introducing for the first time a perfluorinated alkanoate side chain functionalized poly(3,4-ethylenedioxythiophene) (PEDOTF) as a hydrophobic SC in potassium-selective electrodes (K-SCISEs) based on plasticized poly(vinyl chloride). The SC incorporates the tetrakis(pentafluorophenyl)borate (TFAB–) anion, which is also present as a lipophilic additive in the ion-selective membrane (ISM), thus ensuring thermodynamic reversibility at the SC/ISM interface and improving the potential reproducibility of the electrodes. We show here that the PEDOTF-TFAB solid contact, which was prepolarized prior to the ISM deposition to either its half or fully conducting form (i.e. different oxidation states) in acetonitrile containing 0.01 M KTFAB, had a very stable open-circuit potential and an outstanding potential reproducibility of only ±0.5 mV (n = 6) for 1 h in the same solution after the prepolarization. This shows that the oxidation state of the highly hydrophobic PEDOTF-TFAB film (water contact angle 133°) is stable over time and can be precisely controlled with prepolarization. The SC was also not light sensitive, which is normally a disadvantage of conducting polymer SCs. After the ISM deposition, the standard deviation of the E° of the K-SCISEs prepared on glassy carbon was ±3.0 mV (n = 5), which is the same as that for conventional liquid contact K-ISEs. This indicates that the ISM deposition is the main source for the potential irreproducibility of the K-SCISEs, which has been overlooked previously.

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

“…The bulk CNT modification with octadecane provided a hydrophobic surface with water contact angles of 145±2° (Figure ). Thus the polarity of the OD‐MWCNT surface is a rather close match to that of the PEDOTF‐TFAB film (133°) . Interestingly, this is just a slight increase with respect of the unmodified batch (141±3°) that seem to validate the very frequent use of unmodified CNTs for SCISE preparations.…”

“…For comparison, we found earlier a ca. 2–3 mV standard deviation for the E 0 of conventional liquid contact ISEs . This property of the octadecane functionalized carbon nanotube based SCISEs was not clear despite the fact that such solid contact materials were explored in a number of applications and electrode configurations, e. g., reference electrodes , planar screen‐printed electrodes for measurements in saliva , anion selective electrodes for environmental samples , submersible electrodes in seawater , and intradermal electrodes for interstitial potassium ion detection .…”

“…In Figure 5, a rigorous comparison of the calibration parameters of OD-MWCNT-based K + -SCISEs with the state of the art prepolarized PEDOTF-based electrodes (prepared as reported earlier [31]) reveals very similar analytical performance parameters: log LOD: À 6.3 vs. À 6.3, slope: 57.8 mV/decade (� 0.6) vs. 58.2 (� 0.1) mV/ decade, E 0 (intercept): 460.0 (� 3.6) mV vs. 329.7 (� 2.5) mV. Please note that the slightly larger SD value for the intercept than the reported SD values for the potential stability in a solution with fixed primary ion activity is due to the added uncertainty of the slope.…”

Solid-Contact Ion-Selective Electrodes: Response Mechanisms, Transducer Materials and Wearable Sensors

“…Such a 3D structure offers high redox capacitance to enhance the reproducibility of SC-ISEs. Reprinted with permission from [26], Copyright (2019) American Chemical Society. (D) An ultimate approach by both C14-chain functionalized PEDOT and TPFPhB − doping to improve the performances of SC-ISEs.…”

Unintended Changes of Ion-Selective Membranes Composition—Origin and Effect on Analytical Performance

“…For many years conducting polymers (CPs) have remained one of the most popular transducer materials; a wide range of CPs has been tested—from relatively hydrophilic electropolymerized materials like oxidized polypyrrole [ 27 , 40 , 41 ] or polyaniline [ 42 ] to more hydrophobic solvent processable CPs. Among hydrophobic polymers, alkylpolythiohenes, e.g., poly(3-octylthiophene) [ 43 ] or composites [ 44 ] render hydrophobicity due to the dopant/component applied [ 45 , 46 ], or other systems [ 47 , 48 ]. Although the majority of SC systems proposed use plasticized PVC-based ISMs, other membrane materials.…”