Browsing by Subject "Ion-selective electrode"

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    Improving the Performance of Electroanalytical Devices for Sensing and Energy Storage
    (2016-01) Mousavi, Seyedeh Moloud
    My graduate research was focused on improving the performance and expanding the application of two categories electrochemical devices that are used in energy storage and sensing: electrochemical double-layer capacitors and ion-selective electrodes. The energy density of an electrochemical capacitor is determined by ½ CV2, where V is the potential difference between the plates of a capacitor and C is the capacitance density. Therefore, extending the operational voltage of such devices, which is limited by the electrochemical window of the electrolyte, can improve the device energy density. Optimizing the structure and improving electrochemical stability of electrolytes that can be utilized in electrochemical capacitors, was one of the goals of research presented in this thesis. Chapter 2 reviews the conventional methods for quantifying the electrochemical stability of electrolytes, and discusses their limitations. A new method for quantifying electrochemical stability of ionic liquids and electrolytes is suggested and several advantages of the proposed method is demonstrated for variety of systems. The effect of electrolyte structure on its electrochemical stability and accessible potential window is discussed in Chapter 3 and Chapter 4 highlights advantages of application of ionic liquids as electrolytes in electrochemical capacitors. Ion-selective electrodes, ISEs, are electrochemical sensors that determine the concentration of a wide range of ions and are used for billions of measurements in clinical, environmental, and chemical process analyses every year. However, two factors limit the application of ISEs in biological analyses: (1) Interference of biological molecules (2) Large sample volumes needed for ISE measurements. Recently, fluorophilic compounds have been applied in the ion-selective membrane of ISEs in an effort to reduce the interference of biological molecules. Chapters 5 to 7 show the reliability of sensing with fluorous-phase ion-selective electrodes in the environmental and biological samples. A part of my thesis research is focused on reducing the sample volume needed for detection with these sensors. This goal was achieved by development of highly fluorophilic electrolytes which were used to decrease the resistivity of the fluorous sensing membranes, allowing fabrication of fluorous-phase µ-ISEs and significantly decreasing the sample volume required for sensing.
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    Miniaturizable Ion-Selective Electrode System: Solid Contact Electrode and Liquid Junction Free Reference Electrode
    (2014-05) Zou, Xu
    Ion-selective electrodes (ISEs) are widely used as important, analytical tools to determine the concentration of a broad range of ions for clinical analysis. As a potentiometric sensor, an ISE is comprised of two major parts: an ion-selective electrode and a reference electrode, both of which are vital in guaranteeing accurate and reliable measurement results. Conventional ISEs have an interior solution that forms a liquid contact with a selective membrane. However, complications due to evaporation and freezing in certain circumstances lead to irreproducibility, instability of the signals, and shortened life expectancy. In addition, miniaturization is an obstacle for this type of electrode. A universal method for a solid contact electrode that is calibration-free, durable, reproducible, and inexpensive to fabricate. A plasticized poly(vinylchloride) doped with tris(1,10-phenanthroline) cobalt(2+) tetrakispentafluorophenylborate and tris(1,10-phenanthroline) cobalt(3+) tetrakispentafluorophenylborate has been developed as a transducer layer. This layer has shown very reproducible potential in potassium chloride solutions with a potentil of standard deviation of 0.5 mV and response slope of 61mV / decade to varying concentrations. A redox buffer platform, based on the more lipophilic redox buffer consisting of the Co(III) and Co(II) complexes of 4,4'-dinonyl-2,2'-bipyridyl, was developed and applied to K+, Na+, Ca2+, H+, and CO32- with emf values of an electrode-to-electrode standard deviation as low as 0.7 mV (2% error in concentration) The reference electrode must maintain a constant potential over long periods of continuous measurements. Used in real life samples, salt bridges for conventional reference electrodes clog with proteins and lipids, suffer from contamination by sample components. A new method was developed that involves the application of a current pulse to a hydrophobic ion-doped membrane, thereby controlling transmembrane ion fluxes to obtain a sample independent reference electrode potential. The concentration of the ions released into the sample depended on the current amplitude and length and can be explained quantitatively by diffusion theory. The observable stability of the potential exhibited in this study by reference electrodes exposed to serum was particularly promising in view of biological and medical applications that require long term monitoring.