Potentiometric Selectivities of Ionophore-Doped Ion-Selective Membranes: Concurrent Presence of Primary Ion or Interfering Ion Complexes of Multiple Stoichiometries

Ibrahim Yilmaz, Li D. Chen , Xin V. Chen, Evan L. Anderson, Rosenildo Da Costa, John A. Gladysz, Philippe Bühlmann

    Research output: Contribution to journalArticlepeer-review

    12 Downloads (Pure)

    Abstract

    The selectivities of ionophore-doped ion-selective electrode (ISE) membranes are controlled by the stability and stoichiometry of the complexes between the ionophore, L, and the target and interfering ions (Izi and Jzj, respectively). Well-accepted models predict how these selectivities can be optimized by selection of ideal ionophore-to-ionic site ratios, considering complex stoichiometries and ion charges. These models were developed for systems in which the target and interfering ions each form complexes of only one stoichiometry. However, for a few ISEs, the concurrent presence of two primary ion complexes of different stoichiometries, such as ILzi and IL2 zi, was reported. Indeed, similar systems were probably often overlooked and are, in fact, more common than the exclusive formation of complexes of higher stoichiometry unless the ionophore is used in excess. Importantly, misinterpreted stoichiometries misguide the design of new ionophores and are likely to result in the formulation of ISE
    membranes with inferior selectivities. We show here that the presence of two or more complexes of different stoichiometries for a given ion may be inferred experimentally from careful interpretation of the potentiometric selectivities as a function of the ionophore-to-ionic site ratio or from calculations of complex concentrations using experimentally determined complex stabilities. Concurrent formation of JLzj and JL2 zj complexes of an interfering ion is shown here to shift the ionophore-to-ionic site ratio that provides the highest selectivities. Formation of ILn-1 zi and ILn zi complexes of a primary ion is less of a
    concern because an optimized membrane typically contains an excess of ionophore, but lower than expected selectivities may be observed if the stepwise complex formation constant, KILn, is not sufficiently large and the ionophore-to-ionic site ratio does not markedly exceed n.
    Original languageEnglish
    Pages (from-to)2409-2417
    JournalAnalytical Chemistry
    Volume91
    Issue number3
    Early online date4 Jan 2019
    DOIs
    Publication statusPublished - 5 Feb 2019

    Keywords

    • ion-selective electrode (ISE) membranes
    • ionophore-doped
    • fluorous
    • flourous membranes
    • perfluorinated

    Fingerprint

    Dive into the research topics of 'Potentiometric Selectivities of Ionophore-Doped Ion-Selective Membranes: Concurrent Presence of Primary Ion or Interfering Ion Complexes of Multiple Stoichiometries'. Together they form a unique fingerprint.

    Cite this