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Abstract The main objective of this work is to develop new methods for the determination of Cr(VI), Mo (VI) and U(VI) in ground water and rocks using striping voltammetry and derivative spectrophotometry. Stripping voltammetry, have important advantages such as high sensitivity, low detection limit, relative simplicity and low cost of equipment and automatic on-line and portable options, for the determination of metals at trace levels. Derivative spectrophotomtery offers greater selectivity than does normal spectrophotomtery , because it decreases spectral overlap and allows better resolution. Chromium is widely distributed in nature, hexavalent chromium(VI) is a potential carcinogenic agent , moreover it has become one of the main pollution sources for environment. Consequently, the accurate determination of chromium(VI) is important for monitoring environmental pollution and for quality control of industrial products. Molybdenum is a biologically and physiologically significant element. Due to its unique properties and its importance in nature, Mo has been the subject of a great deal of attention in terms of developing new methods for its determination. It is well known that uranium is toxic as well as being radioactive; the safety profiles for uranium compounds are well established. Because uranium is a relatively mobile element in many surface or near-surface environments, its geochemical exploration methods require the measurement of the trace quantities of the metal ion in water samples, along with that in plants, soils, and rocks. The present study is undertaken, hopefully, to cover the subject of interest and to present some thorough work on direct voltammetric and spectrophotometric determination of chromium , molybdenum and uranium content of ground water and rocks samples. In any case, here it is for the benefit of any one who would like to make use of it. The thesis comprises five main chapters. In addition, the aim of the work, summary and a list of references are included. Chapter One: In the first chapter an introductory section is given including, properties of heavy metals under investigation, stripping analysis measurements and derivative spectrophotometry. General survey of the voltammetric and spectrophotometric determinations of Cr(VI), Mo(VI) and U(VI) is given. The literatures showed that, no studies have yet been reported demonstrating the solution equilibria of chromium, molybdenum and uranium with any of the reagents used in this study or the use of these reagents for voltammetric and spectrophotometric determination of chromium, molybdenum and uranium. Recently, our newly article entitled ”Determination of uranium(VI) in underground water and rock samples by adsorptive cathodic stripping voltammetry” has been accepted for publication in El-Minia Science Bulletin, 2013,24(1),1-23. Chapter Two: This chapter, describes the experimental details of the preparation of solutions needed to analysis of the water and rock samples. Instrumentation and working procedures are also described. Chapter Three: This chapter includes the results and discussion of the voltammetric analyses of the three metal ions under investigation in the water and only uranium(VI) in rock samples was determined using standard addition method. This method is applied to minimize the interferences (if any) and to measure the signal of the total metal content under the same environment of the sample. Plotting the currents signal against the metal ion concentration added to the sample gave straight lines. from this linear relationship, the concentrations, the standard deviation and correlation coefficient values were obtained. In what follows are the conditions of the determination of metal ions under consideration. This method depends on increasing the concentration of the metal onto the electrode surface by adsorption phenomena. The optimum conditions were adjusted to obtain the highest reduction peak signal and resolution for these metal ions in different samples. (a) Cr(VI) was determined by cathodic linear sweep stripping voltammetry (CLSSV) using a mixture of 7.5 X10-3M potassium nitrate as supporting electrolyte and 10 mM mono and disodium hydrogen phosphate as buffer solution pH~7 at accumulation potential + 0.05V vs. Ag/AgCl sat’KCl. (b) Mo(VI) was determined by differential pulse anodic stripping voltammetry (DPASV) using a mixture of 7.5 X10-3M potassium nitrate as supporting electrolyte and 10 mM mono and disodium hydrogen phosphate as buffer solution pH~7 at preconcentration potential -0.6V vs. Ag/AgCl sat’KCl. (c) U(VI) was determined by differential pulse cathodic stripping voltammetry (DPCSV), using a 1 X10-2M solution of sodium perchlorate as a supporting electrolyte and potassium hydrogen phthalate as a buffer solution pH~7 at accumulation potential of -0.4V vs. Ag/AgCl sat’KCl. The results indicate that the concentration of metal ions content in water samples is less than permissible value as given by EPA, Canadian Drinking Water Quality, and the World Health Organization’s guideline. Chapter Four: This chapter in cludes the results and discussion of the spectrophotometric study of the acid-base equilibria of Purpurogallin in aqueous solutions containing 40% (v/v) ethanol. The spectral changes are explained in terms of shifts in equilibria amongst different molecular and ionic species existing in solutions. The ionization constants corresponding to the various acid-base equilibria have been determined. Also the results of the complexation reactions of Cr(VI), and Mo(Vl) with Purpurogallin have been discussed. The composition, molar absorptivities, equilibrium constants and stability constants of the chelates of this reagent were determined. The absorption spectra of solutions with equimolar concentrations of metal ion and the ligand or with an excess of one component were recorded at different pH values in 40% (v/v) ethanol medium. A rapid and sensitive method has been proposed for simultaneous determination of Cr(VI) and Mo(Vl) in their binary mixture using derivative ratio spectra and zerocrossing techniques. The proposed method has been applied successfully for simultaneous determination of Cr(VI) and Mo(Vl) content of some rocks . Chapter Five: This chapter includes the results and discussion of the spectrophotometric study of the acid-base equilibria of Pyrocatechol Violet in aqueous solutions containing 40% (v/v) ethanol. The spectral changes are explained in terms of shifts in equilibria amongst different molecular and ionic species existing in solutions. The ionization constants corresponding to the various acid-base equilibria have been determined. Also the results of the complexation reactions of U(VI), and Mo(Vl) with Pyrocatechol Violet have been discussed. The composition, molar absorptivities, equilibrium constants and stability constants of the chelates of this reagent were determined. The absorption spectra of solutions with equimolar concentrations of metal ion and the ligand or with an excess of one component were recorded at different pH values in 40% (v/v) ethanol medium. A rapid and sensitive method has been proposed for the determination of U(VI) or Mo(VI) in the presence of Fe(III) and V(V) in their ternary mixture using derivative ratio spectra, zero-crossing technique. The proposed method has been applied successfully for determination of U(VI) or Mo(VI) content of some rocks. |