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)₄R_f8]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: logK_H, K^pot = – 11.6; logK_H, Na^pot = – 12.4; logK_H, Ca^pot < – 10.2). The use of the N[(CH₂)₄R_f8]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)₄R_f8]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.