Browsing by Author "Mehretie, Solomon"

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    Comparison of Potentiometric Sensors with Amperometric Sensors for Determination of Nitrate
    (Addis Ababa Universty, 1999-06) Mehretie, Solomon; Hundhammer, B.(PhD)
    A potentiometric sensor based on a membrane-stabilized interface between two immiscible liquids has been developed. It has been tested in both stationary and flow conditions for the determination of nitrate. The selectivity of the sensor based on the concept of ion exchange has been studied. On the other hand, an amperometric flowthrough sensor based on nitrate transfer across the interface of two immiscible electrolyte solutions has been developed. The sensor was applied in a flow injection system for the determination of nitrate ion in tap water. The results from both sensors (potentiometric and amperometric) are in the same range (2.5 - 4.5 mg I"). The results also agreed with measurements conducted using a UV-detector
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    Conducting Polymer and Zeolite Modified Carbon Electrodes for the Determination of Drugs and Biological Fluids
    (Addis Ababa University, 2013-05) Mehretie, Solomon; Tessema, Dr. Merid
    Electrochemical signals can be enhanced by specifically modifying electrode surfaces with the aim of providing suitable environment to the analyte of interest. Poly(3,4- ethylenedioxythiophene) and activated iron(JlI) doped zeolite were used to modify carbon electrodes for the determination of drugs and biological fluids. 3,4- Ethylenedioxythiophene was electropolymerized on glassy carbon electrode by running multi-sweep cyclic voltammetry whereas iron(lIl) doped zeolite was coated on the electrode surface. Both modified carbon electrodes were characterized by using cycl ic voltammetry. The poly(3,4-ethylenedioxythiophene) modified electrodes were employed for the determination of niclosamide and N-acetyl-p-aminophenol while the iron(JlI) doped zeolite modified electrodes were used to determine pyridine-2-aldoxime methochloride and uric acid. Cyclic voltammetry and differential pulse voltammetry were used to investigate the electrochemical behavior of N-acetyl-p-aminophenol and its degradation product, p-aminophenol at poly(3,4-ethylenedioxythiophene) modified electrode in pH 7.0 buffer solution. Both N-acetyl-p-aminophenol and p-aminophenol showed quasi-reversible redox reactions with formal potentials of 367 m V and 101 m V (versus Ag/ AgCI), respectively. The significant peak potential difference (266 m V) between N-acetyl-p-aminophenol and p-aminophenol enabled the simultaneous III determination of these species using differential pulse voltammetry. The voltammetric responses gave linear ranges of 1.0- 100 /lM and 4.0- 320 /lM, with detection limits of 0.40 /lM and 1.2 /lM for N-acetyl-p-aminophenol and p-aminophenol, respectively. Furthermore, the poly(3 ,4-ethylenedioxythiophene) modified electrode showed a very good electrochemical behavior for niclosamide with a significant enhancement of the peak current compared to the bare electrode. A linear voltammetric response for niclosamide was obtained in the concentration range 0.075- 7.50 /lM, with a detection limit of 0.01 /lM. When the iron(lll) doped zeolite modified glassy carbon electrode was treated with sulfuric acid (2.5 mM), it showed a better electrochemical response compared to the untreated zeolite modified electrode. Cyclic voltammetry and square wave voltammetry were employed to investigate the electrochemical behavior of pyridine-2-aldoxime methochloride and uric acid at the modified electrode. The analytical performance of the modified electrode was evaluated using anodic stripping voltammetry in a buffer solution (PH 7.0), and a linear response for pyridine-2-aldoxime methochloride was obtained in the concentration range 0.5-100.0 /lM with a detection limit of 0.16 /lM. The iron(IIl) doped zeolite was also responsible for the electrocatalytic oxidation of uric acid in a buffer solution (PH 4.6). The analytical performance of the iron(IIl) doped zeolite modified electrode was evaluated using square wave voltammetry. A linear anodic response for uric acid in the concentration range 0.6-6.0.0 /lM, a detection limit of 0.09 /lM and sensitivity of 0.64 /lA /lM- 1 were obtained. Finally, the proposed methods were successfully applied for the determination of the analytes in pharmaceutical formulations and/or biological samples.