Potential reproducibility of potassium-selective electrodes having perfluorinated alkanoate side-chain functionalized poly(3,4-ethylenedioxytiophene) as hydrophobic solid contact

The irreproducibility of the standard potential (E⁰) is probably the lastmajor challenge for the commercialization of solid-contact ion-selectiveelectrodes (SCISEs) as single use or wearable sensors. To overcome this issue,we are introducing for the first time a perfluorinated alkanoate side-chainfunctionalized poly(3,4-ethylenedioxythiophene) (PEDOTF) as a hydrophobic SC inpotassium-selective electrodes (K-SCISEs) based on plasticized poly(vinylchloride). The SC incorporates the tetrakis(pentafluorophenyl)borate (TFAB^-)anion, which is also present as a lipophilic additive in the ion-selectivemembrane (ISM), thus ensuring thermodynamic reversibility at the SC/ISMinterface and improving the potential reproducibility of the electrodes. Weshow here that the PEDOTF-TFAB solid contact, which was pre-polarized prior tothe ISM deposition either to its half- or fully conducting form (i.e. different oxidation states) inacetonitrile containing 0.01 M KTFAB, had a very stable open-circuit potentialand an outstanding potential reproducibility of only ±0.5 mV (n=6) for 1 h inthe same solution after the pre-polarization. This shows that the oxidationstate of the highly hydrophobic PEDOTF-TFAB film (water contact angle 133°) is stable over time and can be precisely controlled withpre-polarization. The SC was not either light sensitive that is normally adisadvantage of conducting polymer SCs. After the ISM deposition, the standarddeviation of the E⁰ of theK-SCISEs prepared on glassy carbon was ±3.0 mV (n=5), which is thesame as for conventional liquid contact K-ISEs. It indicates that the ISMdeposition is the main source for the potential irreproducibility of theK-SCISEs, which has been overlooked previously.