Fluorous-Phase Ion-Selective pH Electrodes: Electrode Body and Ionophore Optimization for Measurements in the Physiological pH Range

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Abstract

Because of their low polarity and polarizability, fluorous sensing membranes are both hydrophobic and lipophobic and exhibit very high ion selectivities. Here, we report on a new fluorous-membrane ion-selective electrode (ISE) with a wide sensing range centered around physiologically relevant pH values. The fluorophilic tris[perfluoro(octyl)butyl]amine (N[(CH2)4Rf8]3) was synthesized and tested as a new H+ ionophore using a redesigned electrode body that provides excellent mechanical sealing and much improved measurement reliability. In a challenging 1 M KCl background, these fluorous-phase ISEs exhibit a sensing range from pH 2.2 to 11.2, which is one of the widest working ranges reported to date for ionophore-based H+ ISEs. High selectivities against common interfering ions such as K+, Na+, and Ca2+ were determined (selectivity coefficients: logKH, Kpot = - 11.6; logKH, Napot = - 12.4; logKH, Capot < - 10.2). The use of the N[(CH2)4Rf8]3 ionophore with its -(CH2)4- spacers separating the amino group from the strongly electron-withdrawing perfluorooctyl groups improved the potentiometric selectivity as compared to the less basic tris[perfluoro(octyl)propyl]amine ionophore. The use of N[(CH2)4Rf8]3 also made the ISE less prone to counter anion failure (i.e., Donnan failure) at low pH than the use of tris[perfluoro(octyl)pentyl]amine with its longer -(CH2)5- spacers, which more effectively shield the amino center from the perfluorooctyl groups. In addition, we exposed both conventional plasticized PVC-phase pH ISEs and fluorous-phase pH ISEs to 10% serum for 5 days. Results show that the PVC-phase ISEs lost selectivity while their fluorous-phase counterparts did not.

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Chen, X. V., Mousavi, M. P. S., & Bühlmann, P. (2020). Fluorous-Phase Ion-Selective pH Electrodes: Electrode Body and Ionophore Optimization for Measurements in the Physiological pH Range. ACS Omega, 5(23), 13621–13629. https://doi.org/10.1021/acsomega.0c00582

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