الفهرس 
GENERAL INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Catalytic methods of analysis are very popular examples for the application of kinetics in analytical chemistry. Their sensitivities are generally orders of magnitude higher than conventional equilibrium methods. Therefore, they found recent widespread applications in many fields; especially in the analysis and monitoring of environmental pollutants.
The presence of trace amounts of vanadium, iodide, mercury (II), oxalate, iron(III) and nitrite ions in potable waters and preserved food samples is objectionable owing to their toxic, mutagenic and/or carcinogenic effects. Therefore, ultra sensitive determination of the exact levels of these species in natural waters and preserved foodstuffs, e.g. canned meats, is of great importance for agricultural, environmental, biochemical and health concerns especially in the light of the increased ratio of citizens suffering from complications of cancer in many countries.
In the present dissertation, five new catalytic spectrophotometric and potentiometric methods were developed for trace level determination of vanadium, nitrite, (iodide& mercury), oxalate and Iron (III).
First Method; A novel, highly sensitive, simple and selective kinetic spectrphotometric method was developed for the determination of vanadium based on its catalytic effect on the oxidation of 2,3,4-trihydroxybenzoic acid (THBA) with bromate. The reaction was followed spectrophotometrically by tracing the oxidized product at 412 nm after 31 min of mixing the reagents. The optimum reaction conditions were;1.2 mmol l-1 THBA, 21 mmol l-1
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bromate and 51 mmol l-1 dichloroacetate buffer of pH 1.51.1.12 at 31 oC. Addition of 5 mmol l-1 citric acid enhanced the selectivity of the proposed method. Following the recommended procedure, vanadium ((V) and (IV)) can be determined with a linear calibration graph up to 1.21 μg l-1 and a detection limit, based on the 3Sb-criterion, of 1.111 μg l-1. The high sensitivity and selectivity of the proposed method allowed its direct application to the determination of vanadium ((V) and (IV)) in rain water, rice and wheat samples. The method was validated by comparison with a reference extraction ICP-OES method along with recovery experiments. Moreover, published catalytic-spectrophotometric methods for the determination of vanadium, during the past decade, were reviewed.
Second Method; A modification of AOAC Method 213.31 is proposed to improve the extraction efficiency of nitrite from cured meat samples and its subsequent quantification based on the diazotization-coupling reaction of sulfanilamide with N (1-naphthyl)ethylenediamine dihydrochloride (NED). The various experimental parameters were thoroughly investigated. A 5 g meat sample was mixed with 411 ml water; the pH of the mixture was adjusted to 5.5
± 1.3 and allowed to stand for 2 h on a water bath at 218C, with occasional shaking for the complete extraction of nitrite. After quantitative filtration, an aliquot was mixed with chloroacetic/chloroacetate buffer, pH 1.21 ± 1.15, sulfanilamide, and NED, and the absorbance of the resulting azodye was recorded at 541 nm against water as a reference. Following the recommended procedure, a linear calibration graph was obtained for up to 1.2 μg ml-1 NO2
–, with a correlation coefficient of 1.2222 and a detection limit (based on the 3 Sb-criterion) of 5.2 ng/ml NO2
–. The proposed method was conveniently applied to various cured meat samples and was validated by comparison with the original AOAC method and by recovery experiments that gave quantitative results (24–
229) with convenient reproducibility. Statistical analysis of the analytical data could not detect any systematic error and revealed the high accuracy and precision of the proposed method.
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Third Method; A new highly sensitive, selective, and simple kinetic spectrophotometric method was developed for the determination of trace amounts of iodide ions based on its catalytic effect on the perphenazine (PPZ)-H2O2 redox reaction. The reaction was followed spectrophotometrically by tracing the oxidation product at 522 nm, within 21 seconds of mixing the reactants. The optimum reaction conditions were PPZ (1.21 mmol l-1), H3PO4
(5.11 mol l-1), and H2O2 (2.24 mol l-1) at 31 oC. Following the recommended procedure, iodide was determined with a linear calibration graph up to 2.41 ng ml-1 I-. The detection limit, based on the 3Sb criterion was 1.14 ng ml-l I-. The method was also applied to the determination of iodate and periodate ions with an average recovery of 22.2 %. The method was successfully applied to rain and ground water, table salt, sausage, cow’s milk and raw egg samples. Mercuric ions were determined based on its inhibitory effect on the PPZ-H2O2
reaction catalyzed by I- ions. The reaction was also followed spectrophotometrically at 522 nm, within 21 seconds of mixing the reactants under the same experimental conditions for the determination of 2 ng ml-l I-. Following the recommended procedure, mercuric ions have been determined with a linear calibration graph for up to 1.21 ng ml-1 Hg (II) and a detection limit, based on the 3Sb criterion, of 1.13 ng ml-l Hg (II) and the method was successfully applied to samples of ground water, canned tuna and certified reference materials of dogfish tissues.
Fourth Method; An improved highly sensitive and simple catalytic spectophotometric method for determination of nano amounts of oxalate was developed. The method is based on the catalytic effect of oxalate on the oxidation of Mn(II) to MnO4
- by periodate in concentrated acetic acid media. the fixed time method was used to follow the reaction at 512 nm ( max. of KMnO4) after 5 min. at 31 oC . Under the optimum conditions of 42 μg ml-1
Mn(II), 1.5 mol l-1 acetic acid and 3 mmol l-1 NaIO4 the calibration graph was linear up to 21 ng ml-1 of oxalate and the detection limit (3/S) was 5 ng ml-1.
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Glycine was used as an activator whereas, 1.15 mg/ml of sodium hexameta phosphate was used to completely prevent the precipitation of Mn(IV). The proposed method was applied successfully for the determination of oxalate concentration in a synthetic mixture and well water samples .
Fifth Method; Trace amount of iron(III) can be determined by using its catalytic effects on the hydrogen peroxide-iodide reaction in the acidic environment. The reaction rate was followed by measuring the concentration of iodide ion by means of an iodide ionselective electrode. The most suitable concentrations of hydrogen peroxide, potassium iodide, and hydrochloric acid was found to be 1.12 mol l-1, 1.1 mmol l-1, 1.55 mol l-1. The calibration graph with good proportionality were obtained in the range of 5 to 121 μmol l-1 for iron (III). The proposed method was applied for the determination of Iron (III) concentration in a synthetic mixture and ground water samples directly by using the calibration method.