Semifluorinated Polymers and Hydrophilic High Capacity Ion-Exchangers as Ion-Sensing Membranes for Measurements in Harsh Sample Conditions

Abstract

The research presented in this thesis is focused on the development and use of ion-selective electrodes (ISEs) in harsh conditions, such as measurements in organic solvents, biological media, and samples containing lipophilic ions and at high temperatures. This thesis focuses on the study of two classes of ISE membranes to overcome challenges presented by these conditions, semifluorinated polymer membranes and hydrophilic high capacity ion-exchanger (HHCIE) membranes. First, a brief overview of the working mechanism and components of ISEs, as well as the problems caused by harsh sample conditions is given. Also, included is a discussion on fluorous membrane ISEs, which show resistance to biofouling, HHCIE membranes and polymer background relevant to ISEs. Semifluorinated polymers were synthesized by attachment of fluorinated side chains to the lipophilic polymer, poly(4-vinylphenol). However, the percent conversions of these reactions are not high enough to produce polymers that are suitable for use as ISE membranes. Several semifluorinated monomers were synthesized, polymerized into semifluorinated polymers and then fabricated into ISEs. These electrodes can utilize both fluorophilic and lipophilic ionophores, allowing for a wider range of possible analyte ions then previously available to fluorous membrane ISEs. Ion-exchanger electrodes made from these polymers show a wide selectivity rage, up to 14 orders of magnitude. Study of HHCIE membranes found them to be highly resistant to the effect of Donnan failure (co-ion interference). HHCIE membranes were used to make a sensor that could monitor the concentration of NOX- species in situ during nanoparticle synthesis reactions at 150 ºC in propylene glycol. It is also shown that nitrate ions present in this reaction are reduced to nitrite. A current pulse reference electrode with a HHCIE membrane was developed which should have advantages over similar electrodes made with lipophilic membranes when measuring in biological media.