Potentiometric Sensors Based on Fluorous Membranes Doped with Highly Selective Ionophores for Carbonate

Abstract

Manganese(III) complexes of three fluorophilic salen derivatives were used to prepare ion-selective electrodes (ISEs) with ionophore-doped fluorous sensing membranes. Because of their extremely low polarity and polarizability, fluorous media are not only chemically very inert but also solvate potentially interfering ions poorly, resulting in a much improved discrimination of such ions. Indeed, the new ISEs exhibited selectivities for CO32− that exceed those of previously reported ISEs based on non-fluorous membranes by several orders of magnitude. In particular, the interference from chloride and salicylate was reduced by two and six orders of magnitude, respectively. To achieve this, the selectivities of these ISEs were fine-tuned by addition of non-coordinating hydrophobic ions (i.e., ionic sites) into the sensing membranes. Stability constants of the anion–ionophore complexes were determined from the dependence of the potentiometric selectivities on the charge sign of the ionic sites and the molar ratio of ionic sites and the ionophore. For this purpose, a previously introduced fluorophilic tetraphenylborate and a novel fluorophilic cation with a bis(triphenylphosphoranylidene)ammonium group, (Rf6(CH2)3)3PN+P(Rf6(CH2)3)3, were utilized. The optimum CO32− selectivities were found for sensing membranes composed of anionic sites and ionophore in a 1:4 molar ratio, which results in the formation of 2:1 complexes with CO32− with stability constants up to 4.1 × 1015. As predicted by established theory, the site-to-ionophore ratios that provide optimum potentiometric selectivity depend on the stoichiometries of the complexes of both the primary and the interfering ions. However, the ionophores used in this study give examples of charges and stoichiometries previously neither explicitly predicted by theory nor shown by experiment. The exceptional selectivity of fluorous membranes doped with these carbonate ionophores suggests their use not only for potentiometric sensing but also for other types of sensors, such as the selective separation of carbonate from other anions and the sequestration of carbon dioxide.

Ion-Selective Electrodes with Unusual Response Functions: Simultaneous Formation of Ionophore–Primary Ion Complexes with Different Stoichiometries

“…This method 29,53,54 was already used in the past to determine complex stabilities in fluorous membranes. 43,45,48 For the purpose of this work, tetraphenylphosphonium (PPh 4 + ) was chosen as the ion that does not form complexes with the ionophore.…”

Cleaning of pH Selective Electrodes with Ionophore‐doped Fluorous Membranes in NaOH Solution at 90 °C

“…We found that fluorous systems exhibit substantially improved ion selectivities as compared to non‐fluorous ISE membranes, which has also resulted in remarkably low detection limits . Electrodes with fluorous membranes have been successfully applied for the detection of several analytes, not only in simple aqueous samples but also in biologically relevant systems such as bacterial growth media, lake and river water containing natural organic matter, and Ottawa Sand suspensions . Here we discuss the lifetime of pH sensors with ionophore‐doped fluorous sensing membranes when exposed to hot caustic solutions as they are used in CIP treatments.…”

Collective fluorescence switching of counterion-assembled dyes in polymer nanoparticles

“…In pure form, such salts were described as 'frozen ionic liquids' with appreciable fluorescence, which confirms that the counterion can prevent p-stacking of the dyes 25,26 . The tetraphenyl borate (TPB) anion and its fluorinated analogues, used as ionophores in polymeric cation-sensitive electrodes 27,28 , are particularly interesting counterions due to their bulky tetrahedral structure. However, so far, no attempts were made to use TPBs for encapsulation of cationic dyes into polymer NPs.…”