The rational design of anion-selective potentiometric sensors

The objective of this work was to develop ion-selective electrodes (ISEs) for targeted oxoanions using a biomimetic approach. Proteins can coordinate with oxoanions through the guanidinium moiety of arginine. Several compounds containing the guanidinium functional group were tested in ISE membranes and demonstrated unique selectivity towards specific oxoanions.; A hydrogen sulfite-selective electrode was developed by incorporating a guanidinium receptor into an ISE membrane. The electrode did not respond significantly to other anions and had a linear response to HSO{dollar}sb3{dollar}- over four decades of concentration. An {dollar}sp1{dollar}H-NMR titration was performed to identify the hydrogen sulfite/ionophore complex stoichiometry in this HSO{dollar}sb3{dollar}- sensor. Additional guanidinium ionophores tested were found to be selective for the oxoanion salicylate. Small changes to the structure of one salicylate ionophore led to a receptor with enhanced response characteristics towards salicylate. The ability to design selective ionophores using a biomimetic strategy, and to alter response characteristics through structural changes to an ionophore has been demonstrated.; An SO{dollar}sb2{dollar} gas sensor was designed using the developed HSO{dollar}sb3sp-{dollar}-selective electrode behind a gas permeable membrane (GPM). This sensor demonstrated a superior selectivity compared with the conventional Severinghaus-type SO{dollar}sb2{dollar} gas sensor. The detection limit was also improved over that of the Severinghaus sensor through a pH trap effect. The excellent selectivity of the HSO{dollar}sb3sp-{dollar} electrode, along with the ability of the GPM to discriminate gaseous and non-gaseous species, combine to generate the most selective potentiometric SO{dollar}sb2{dollar} gas sensor reported to date.; The development of selective oxoanion electrodes was also achieved by use of an electrochemical imprinting technique. Nitrate ISEs have been developed by electropolymerizing pyrrole onto electrodes in the presence of NaNO{dollar}sb3{dollar}. Electrochemical variables were optimized to improve the potentiometric response of the electrodes, and near-Nernstian slopes for nitrate were observed over four decades of concentration. These developed nitrate electrodes achieved selectivity coefficients that were improved by as much as four orders of magnitude compared to commercially available nitrate ISEs. Finally, the use of electrochemical polymerization in the preparation of ISE films was shown to be a viable way to achieve electrodes with extended service lives.