الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Nanotechnology has shown a great potential in different applications that are widely used in our life. One of these applications is the bio-sensors that have high sensitivity. Solid electrodes based on carbon are currently widespread use in electroanalysis because of their broad potential window, low background current, rich surface chemistry, low cost, and chemical inertness. However, their sensitivity is relatively poor towards the determination of some biologically active compounds and metal ions. This may be attributed to its high surface hydrophobicity, which is mainly responsible for high overpotential (irreversibility) and sluggishness of the kinetics of the electrode process, resulting in weak electrochemical responses. A fascinating and effective way to improve the sensitivity is to find a good modifier to increase the rate of electron transfer (on one side), surface area and consequently the adsorptive affinity of the surface of carbon electrodes (on another side). The work in this thesis aimed to prepare different types of bio-sensors and elucidate the electrode reaction pathways of some biologically active compounds {Duloxetine HCl (DXT.HCl), Escitalopram oxalate (ESCIT.Oxalate) and Cinacalcet HCl (CIN.HCl)} in buffered solutions of various pH values, and identification of their adsorptive behavior at the unmodified carbon paste electrode (Bare CPE) or that modified with multiwall carbon nanotubes (MW-CNTs) and sodium montomorillonite clay (Na-MMT modified CPE). This work was aimed also to optimize electroanalytical methods for trace determination of the investigated compounds in their bulk forms, formulations and in spiked human serum at the unmodified carbon paste electrode (Bare CPE) or that modified with multiwall carbon nanotubes (MW-CNTs) and sodium montomorillonite clay (Na-MMT modified CPE), (using anodic stripping voltammetry method). Besides the UV-visible spectrophotometric of the investigated compounds are reported. The methods are based on the combination of a preconcentration step with the advanced voltammetric measurement which generates an extremely favorable signal-to-background ratio that characterizes stripping voltammetric analysis. Carbon paste electrode (CPE) is a mixture of an electrically conducting graphite powder and hydrophobic adhesive (organic liquid the binder). It has been extensively used in electroanalytical chemistry because of its excellent properties: wide potential range (from –1.40 to 1.30 V), easy preparation, convenient surface renewal, low residual current, porous surface, and low cost. Often undesirable overpotential at CPEs can be suppressed by means of surface hydrophilization by intensive electrolysis or chemical treatment, erosion by surfactants in situ, or using special modifiers. In spite of the wide range of electrode modifiers, CNTs have ability to hold the potential for wide applications in electrochemistry due to their exquisite tube structure, small dimensions, high surface area, high electrical conductivity, unique structures, significant mechanical strength, high thermal properties, and good chemical stability. This made CNTs interesting materials in the fields such as electrochemical sensors, biosensors, supports for heterogeneous metal catalysts in organic synthesis, fuel cells, semiconductors, batteries, random access memory cells, field effect transistor, field emission display, atomic force microscopy probes, microelectrodes, specific adsorbents to remove organic pollutants from water and waste water and as a potential drug carriers in cancer therapy. CNTs-modified electrodes have shown interesting catalytic properties toward electrochemical process since it acts as electrical conducting nanowires between the base electrode and the electroactive-species on the surface. Several of research articles published in recent years report many remarkable claims about the advantages of carbon nanotubes, such as increased voltammetric currents, increased heterogeneous electron-transfer rates, insignificant surface fouling of CNT-based electrodes, and an apparent “electrocatalytic” effect towards the redox process of a wide variety of compounds. Clays have attracted the interest of electrochemists, in particular for their analytical applications. Clay minerals are naturally occurring materials, cheap and widely available. Their welldefined layered structure and flexible adsorptive properties make them interesting materials that can be used as catalysts or catalytic supports, or sorbents for inorganic and organic compounds. Montmorillonite (MMT) clay is of a 2׃ 1 layered structure, a single layer of aluminum octahedral sheet sandwiched between two layers of silicon tetrahedral sheets. Montmorillonite particles carry two kinds of electric charges: a surface charge (a variable (pH dependent) charge resulting from proton adsorption/desorption reactions on the surface of hydroxyl groups) and a structural (permanent) negative charge resulting from isomorphous substitutions within the clay structure. As a consequence of this negative potential, montmorillonite has negative electrophoretic mobility and very important cation adsorption and cation exchange properties. The negative charges of the layers are compensated by cations Ca2+ or alkali-metal ions bounded between the layers. These cations can be exchanged by other inorganic or organic cations. Also, these cations are strongly hydrated in the presence of water to render natural clay hydrophilic. Owing to the hydrophilic environment at the surface and low organic carbon content, natural clay is an effective adsorbent for ionic organic species. On another side, the OH and atoms on the broken edges of montmorillonite hydrolyze and form Lewis acid or Lewis base functional groups that are the sources of the pH-dependent charge. Based on the molecular structure of montmorillonite, cations can also be adsorbed by either electrostatic attraction on the basal plane or formation of covalent bonds with the functional groups on the broken edges. So, MMT has been widely used for modifying electrodes to improve their determination sensitivity towards anions, cations, and organic compounds. The thesis comprises of three main chapters: Chapter I: This chapter contains a general introduction concerning the principles of different voltammetric techniques, types of modifiers, such as multiwall carbon nanotubes (MWCNTs) and sodium montomorillonite clay (Na-MMT modified CPE).