Browsing by Subject "Ion-Selective Electrodes"

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    Development of Improved Ion-Selective and Reference Electrodes for In Situ Monitoring of Ion Concentrations
    (2019-07) Anderson, Evan
    This dissertation is focused on the application of electrochemistry for the fundamental understanding, development, and application of electrochemical sensors. In particular, my research focused on the development and understanding of reference electrodes and ion-selective electrodes for potentiometric sensing applications. Recently, following the needs of point-of-care and wearable sensors, electrode designs have transitioned from bulky devices with an aqueous inner filling solution (e.g. pH electrodes) to planarizable solid-contact electrodes. However, unless their polymeric sensing and reference membranes are held in place mechanically, delamination of the physically adhering membranes limits sensor lifetime, as even minimal external mechanical stress or thermal expansion can result in membrane delamination and, thereby, device failure. To address this problem, we designed a sensing platform based on inexpensive polymers to which membranes are attached covalently through photopolymerization. Even extreme mechanical stress does not result in the delamination of the sensing and reference membranes from the underlying polymer, which results in electrodes that exhibit much improved long-term performance and greatly reduced size. This method of sensor preparation is broadly applicable to a wide range of electrode types and allows for long-term measurements of numerous ions that are of environmental and medical significance. Moreover, the applicability of these ion-selective electrodes for long-term measurements requires reference electrodes that also provide stable responses. Reported here are two types of improved reference electrodes based on capillaries and ionic liquids.
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    Semifluorinated Polymers and Hydrophilic High Capacity Ion-Exchangers as Ion-Sensing Membranes for Measurements in Harsh Sample Conditions
    (2016-01) Carey, Jesse
    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.